This easy chocolate brownie cake is an old-fashioned recipe that gives you the the taste of chocolate walnut brownies in sheet cake form. Just like grandma used to make!
Preheat your oven and grease a large baking sheet.
Mix the flour and sugar in a large bowl and set aside.
Heat a pot over medium-high heat on the stove. Melt butter in pot.
Once melted, add your cocoa powder and water and bring the mixture to a boil.
Add the boiling chocolate mixture to the flour mixture from earlier and stir until well combined.
Add buttermilk, eggs, baking soda, and vanilla to the mixture and combine until you have a nice smooth batter.
Pour the batter into the prepped baking sheet making sure to evenly spread it across the entire sheet pan.
Bake cake in the oven for 20-22 minutes or until cake is cooked all the way through.
Ice cake within five minutes of removing cake from the oven.
Top with chopped walnuts if desired.
Allow cake to cool completely then cut into squares and serve.
Icing
Heat a pot over medium-high heat on the stove. Melt butter in pot.
Add cocoa and milk to melted butter and bring to a boil.
Put your powdered sugar into a small bowl then pour the boiled mixture over the powdered sugar and stir to combine to make your icing.
Notes
Add the walnuts immediately after adding the icing rather than waiting until it hardens. This will keep the nuts from falling off when you slice the cake.Use a spatula to make sure that the chocolate brownie cake batter spreads around the entire sheet pan in one even layer.Leave the chocolate brownie cake in the pan rather than slicing it all and removing for storage. I recommend just covering it with something like this sheet pan lid.Remove the chocolate mixtures from heat as soon as they start boiling, don’t let them keep boiling or you’ll lose some of the moisture in the cake and icing.Use a small rectangle spatula to remove the cake squares from the pan without destroying the rest of the squares.