Chocolate Oatmeal Spider Cake

You probably never thought you’d hear the words chocolate, oatmeal, spider and cake together in a sentence, but now you have, and trust me, it’s an excellent combination!

I shared an apartment with my brother for a number of years and we often partook in culinary adventures together. Mostly I would bake sweet treats, and he would make savoury dishes. I’ll admit, I never thought his concoctions looked particularly appetizing (there were some really questionable looking dips and sauces), but everything he made always tasted great!

He isn’t super big on cake or sweets, but one day he found this recipe online for the The World’s Best Chocolate Oatmeal cake on Pinch of Yum and asked if we could make it together.

We followed the directions exactly, even using the recommended Ghirardelli chocolate chips (which are super good by the way – I use these a lot now). The cake turned out so moist and delicious, and the frosting is unlike anything I have had before! Even my brother was impressed and decided that if he was going to give in and admit to liking any cake, it would be this one.

I’ve made this cake a number of times since, always in the recommended 9″x 13″ cake pan. Last year however, I decided to dress it up a bit for Halloween. I baked the cakes in two 9″ cake pans, and then frosted them, stacked them, and decorated them with colourful smartie spiders!

cake ingredients

The oatmeal makes this cake really moist, but it doesn’t taste oatmealy. To start, you soak quick cooking oats in boiling water to soften them up, and then set them aside to cool.

soaking oatmeal in water

While the oatmeal is soaking, beat the brown and white sugar together with the melted butter until smooth and creamy, and then add the eggs and mix well.

sugar and butter in bowl

sugar, butter and eggs mixed together

Next, add all the dry ingredients to the butter/sugar mixture. I always whisk my dry ingredients together first to help ensure everything is well mixed. A couple of times I’ve mixed up some really thick cookie dough and my mixer has struggled to mix everything thoroughly. I ended up with a pour distribution of baking soda, so half my cookies were really flat and half were really puffy. Now I just always mix my dry stuff together first and I don’t have any issues.

mixed dry ingredients

The batter will be really thick after you add in all the dry ingredients, but it will thin down once you add the oatmeal.

really thick cake batter

After you’ve mixed in the oatmeal, stir in half the chocolate chips and then distribute the batter evenly between two 9″ baking pans (or if you just want to do one big cake, a 9″x13″ pan).

mixed cake batter

Sprinkle the remaining half of the chocolate chips onto the top of the batter before putting the cakes in the oven. The first time I tried this recipe, I stirred all the chocolate chips in at the beginning and found that they sunk to the bottom more. Sprinkling the extras on top ensures a more even distribution of chocolate chips.

cakes ready to go in oven

Bake for about 30-35 minutes or until a tester comes out clean. Once the cakes have cooled enough that you can handle the pans, you can flip them onto a cooling rack to cool completely.

cakes fresh from oven

Wait until the cakes have completely cooled before you start the frosting. This frosting is delicious but it sets insanely fast, so you have to work quickly with it, and be prepared to use it right away.

frosting ingredients

In a medium saucepan melt the butter with the milk and sugar over a medium-low heat. Bring the mixture to a boil and let it boil for 30 seconds.

melted butter and sugar for frosting

Reduce the heat to low and stir in the marshmallows and chocolate chips. Mini marshmallows work best as they melt quicker, but you could use larger marshmallows too. I would still recommend cutting them up smaller though to expedite the melting process.

melting marshmallows for frosting

Keep stirring the frosting until the marshmallows and chocolate chips are fully melted and the mixture is smooth.

frosting cooked and ready for pouring

Now comes the part where you have to work quickly. I mean really quickly! The frosting sets almost instantly. This isn’t a frosting that you spread with a spatula. Instead you pour it over the cake while the frosting is still hot. It will run over the surface of the cake creating a nice, smooth, shiny finish.

You can see from the pictures below how there are sort of layered drips down the sides of the cake. That’s because I didn’t pour the frosting all in one go. I poured a bunch on one cake, then some on the other, and then more on the first cake and the last bit on the second (I had a hard time judging how much was half). If you want it to look really smooth, it’s better to pour it swiftly in one go, but for this spider cake, I kind of like the drippy edges.

pouring the frosting onto the cake

After just a couple of minutes, the frosting should be set enough that you can stack the two cake layers. The surface of the frosting is quite delicate, so it may crack a bit when you move it, but that just adds to the aesthetic.

stacked and frosted cake layers

I used melted white chocolate to create the spider web. I put the melted chocolate into a piping bag and first piped the long lines across the cake, and then piped the spiral afterwards.

close up detail of a spider on the cake

For the spiders I used melted semi-sweet chocolate. I started by piping a little blob where I wanted the spider to go, and then stuck a smartie on top. I then piped another little blob for the spider head, and made eight little legs coming out from the sides.

spider cake

I added a few little webs and spiders coming out from between the two layers to give it a really nice spider infested look. Delicious!

MAKES: two 9″ round cakes, or one 9″x13″ cake
SOURCE: Pinch of Yum


for the Cake
  • 1 cup quick cooking oats
  • 1 3/4 cups boiling water
  • 1 cup brown sugar
  • 1 cup white sugar
  • 1/2 cup butter, melted
  • 2 eggs, lightly beaten
  • 1 3/4 cups flour
  • 1 tsp baking soda
  • 1/2 tsp salt
  • 1 1/2 tbsp cocoa powder
  • 1 x 12 oz bag chocolate chips (divided in half) – (Ideally Ghirardelli milk chocolate)
for the frosting
  • 6 tbsp butter
  • 6 tbsp milk
  • 1 1/2 cups sugar
  • 3/4 cup chocolate chips (Ideally Ghirardelli milk chocolate)
  • 3/4 cup mini marshmallows
  • 1/4 cup white chocolate chips
  • 1/4 cup semi sweet or dark chocolate chips
  • Handful of smarties in assorted colours


Make the cakes
  • Pre-heat your oven to 350°F.
  • Add the boiling water to the oatmeal and let sit until softened and cooled slightly.
  • Meanwhile, beat the butter together with the brown and white sugar.
  • Add the eggs and mix until smooth.
  • In a medium bowl, whisk together the flour, baking soda, salt and cocoa.
  • Add the dry ingredients to the butter/sugar mixture and stir until just combined.
  • Add the oatmeal and mix until incorporated.
  • Stir in half of the chocolate chips.
  • Divide the batter into two greased and floured 9″ cake pans (or a 9″x”13 pan).
  • Sprinkle the remaining chocolate chips on top of the cake batter.
  • Bake for 30-35 minutes or until a tester comes out clean.
  • Let the cakes cool completely before starting on the frosting.

Note: I’ve found this cake tastes best at room temperature the second day. The flavour just seems to peak at that point.

Make the frosting
  • Melt the butter, sugar, and milk in a large saucepan over medium-low heat.
  • Bring the mixture to a boil and let boil for 30 seconds.
  • Reduce the heat to low and then add the chocolate chips and marshmallows.
  • Stir the frosting until completely smooth.
  • Pour the frosting immediately over the cakes (it will set really quickly)
Decorate the cake
  • Once the frosting has set, stack the two 9″ cakes.
  • Melt the white chocolate chips and transfer to piping bag.
  • Pipe the spider web by making long lines, and then piping the spiral.
  • Melt the semi-sweet (or dark) chocolate and transfer to a piping bag.
  • Pipe a blob of dark chocolate where you want the spider to go and stick a smartie on top.
  • Pipe another little chocolate blob to make the spider head, and then pipe four little legs on each spider.
  • Decorate with as many spiders are you like.

3 Replies to “Chocolate Oatmeal Spider Cake”

    1. I have only used the Quaker Quick Oats, as that is usually what I have on hand. I suspect with large flaked oats the texture might be a little different, but I think as long as you soak the oats until they are nice and soft you should be good!

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