Simple Moist Chocolate Walnut Cake

This recipe was originally published in September 2021. It has since been updated with new images.

Sometimes you don't want a layer cake, as much as I love my chocolate orange layer cake, and want something simple like a snack cake! Using my favorite fudgy chocolate sour cream frosting (just like in Matilda's chocolate cake), this chocolate walnut cake is a chocolate lover's dream come true. If you want something even more chocolatey, you have to try my triple chocolate layer cake!

This is a really simple single-layer chocolate cake, so it's perfect to make when you don't have a ton of time. The cake layers are loaded up with finely chopped walnuts, and I added more walnuts on top of the frosting!

Recipe Testing

The base of this chocolate cake is my favorite! It's a dark chocolate cake that is super chocolatey thanks to hot coffee. The coffee isn't flavoring the cake, but it helps 'bloom' the cocoa powder, making the chocolate flavor richer. It's the same chocolate cake as my Matilda's chocolate cake and chocolate cake with chocolate cream cheese frosting, I just added finely chopped walnuts.

Ingredients Needed for Chocolate Walnut Cake

• Oil: Use a neutral oil in the cake, like canola, vegetable or sunflower oil. This will make the cake extra moist and no need to cream butter!
• Coffee: I add hot coffee to the cocoa powder which will bloom it, making the chocolate extra dark and chocolatey!
• Cocoa Powder: I'm using Dutch processed cocoa powder in both the cake and frosting.
• Buttermilk: Using buttermilk in the cake will make it super moist.
• Walnuts: you can swap out walnuts for pecans or hazelnuts. Make sure you chop them up very finely or they'll all sink to the bottom!
• Melted Dark Chocolate: try to use good quality chocolate for the frosting, it will make a huge difference!
• Sour Cream: I don't recommend substituting the sour cream for something else in the chocolate sour cream frosting.

See the recipe card for full information on ingredients and quantities.

Step by Step Instructions

Step One: Whisk together your sugar and egg for 1 minute until you have a few bubbles.

Step Two: Add the buttermilk, hot coffee, oil, vanilla extract and, salt and mix again.

Step Three: Add your cocoa powder and whisk until smooth. Add your flour, baking powder, baking soda and fold until there are no pockets of flour.

Step Four: Stir in the chopped walnuts.

Step Five: Pour into an 8x8 greased and parchment lined pan and bake for 35-45 minutes at 350 degrees Fahrenheit.

Step Six: Let the cake cool in the pan for about 10 minutes, then remove and let cool completely on a wire cooling rack.

Step Seven: Melt the chocolate in a small microwave safe bowl. I recommend doing it in 15 second increments, making sure you stir after every increment so it doesn't burn.

Step Eight: Beat your butter and confectioners' sugar together on low speed in your stand mixer or with a hand mixer until well combined. Turn the speed to high and mix for 2-3 minutes until fluffy.

Step Nine: Add in your cocoa powder and mix on low until the cocoa powder is combined - this stops it from flying everywhere! Increase the speed to medium and mix for 1-2 minutes. Pour in your sour cream, melted chocolate and salt and mix once more.

Step Ten: Spread the chocolate frosting on top of your cooled cake and enjoy!

Expert Tips & Tricks

• Kitchen Scale: I highly recommend using a weighing scale and measuring out your ingredients the metric way. It makes a huge difference to your baking and is the most accurate way to bake!
• Room Temperature: I make sure that all of my ingredients are at room temperature before I start the recipe, so pull out all of the ingredients (including the buttermilk!) before you start baking.
• Walnuts: Make sure your walnuts are finely chopped, I use my food processor to do this but you could also place them in a large ziplock bag and crush them with a rolling pin. If the walnuts are too large, they might sink in the chocolate walnut cake.