Preheat and Prep: Preheat your oven to 350°F (175°C). Grease and flour two 8-inch round cake pans. You can also line the bottoms with parchment paper for easy removal.
Cream the Butter and Sugar: In a large bowl, cream together the softened butter and sugar until light and fluffy.
Add the Eggs: Beat in the eggs one at a time, making sure each is fully incorporated before adding the next. If the mixture looks curdled, add a tablespoon of flour.
Fold in the Dry Ingredients: Gradually fold in the self-rising flour until just combined. Be careful not to overmix, as this can result in a tough cake.
Add the Coffee and Walnuts: Stir in the cooled coffee and chopped walnuts until evenly distributed. The batter should be smooth and fragrant.
Bake: Divide the batter evenly between the prepared cake pans. Bake for 25-30 minutes, or until a wooden skewer inserted into the center comes out clean.
Cool: Let the cakes cool in the pans for 10 minutes before inverting them onto a wire rack to cool completely.
Make the Coffee Buttercream: In a large bowl, cream the softened butter until light and fluffy. Gradually add the confectioners' sugar, beating on low speed until combined. Then, increase the speed and beat for 2-3 minutes until light and airy. Slowly add the cooled coffee, beating until smooth and creamy.
Frost the Cake: Once the cakes are completely cool, spread a generous layer of coffee buttercream over one cake layer, top with the second cake layer, and frost the entire cake.
Decorate: Sprinkle the finely chopped walnuts over the top of the cake for a beautiful finishing touch.