Follow these steps to create your Coffee Walnut Cake:

Preparing the Cake:

1. Preheat the Oven: Preheat your oven to 350°F (175°C). Grease and line two 8-inch round cake pans with parchment paper.
2. Cream the Butter and Sugar: In a large mixing bowl, beat the softened butter and granulated sugar together until light and fluffy, about 3-5 minutes.
3. Add Eggs: Add the eggs one at a time, mixing well after each addition.
4. Combine Dry Ingredients: In a separate bowl, whisk together the flour, baking powder, and salt.
5. Mix Coffee and Vanilla: In a small bowl, combine the brewed coffee and vanilla extract.
6. Combine Wet and Dry Ingredients: Gradually add the flour mixture to the butter mixture, alternating with the coffee mixture, starting and ending with the flour mixture. Mix just until combined.
7. Fold in Walnuts: Gently fold in the chopped walnuts.
8. Bake the Cake: Divide the batter evenly between the prepared cake pans. Bake for 25-30 minutes, or until a toothpick inserted into the center of the cakes comes out clean.
9. Cool the Cakes: Allow the cakes to cool in the pans for 10 minutes, then transfer them to a wire rack to cool completely.

Preparing the Coffee Buttercream Frosting:

10. Dissolve Coffee Granules: Dissolve the instant coffee granules in the milk.
11. Beat Butter and Sugar: In a mixing bowl, beat the softened butter until creamy. Gradually add the powdered sugar and continue to beat until smooth.
12. Add Coffee and Vanilla: Add the dissolved coffee and vanilla extract to the butter mixture, beating until fully combined and fluffy.

Assembling the Cake:

13. Frost the Cake: Place one cake layer on a serving plate. Spread a layer of coffee buttercream frosting over the top. Place the second cake layer on top and frost the top and sides of the cake.
14. Garnish with Walnuts: Sprinkle the finely chopped walnuts over the top of the cake for decoration.