Coffee Walnut Cake: Preheat your oven to 350 degrees F (180 degrees C). Butter, or spray with a non stick vegetable spray, two - 8 inch (20 cm) round cake pans with 2 inch (5 cm) sides. Line the bottoms of the pans with parchment paper.

In a bowl, whisk or sift the flour with the baking powder, baking soda, and salt. 

In the bowl of your electric stand mixer (fitted with the paddle attachment), or with a hand mixer, beat the butter until smooth. Add the sugars and beat on medium-high speed until the mixture is light and fluffy (about 3 minutes). Add the eggs, one at a time, beating well after each addition. Beat in the vanilla extract. Scrape down the sides and bottom of the bowl as needed. With the mixer on low speed, add the flour mixture (in three additions) alternately with the milk and coffee (in two additions), starting and ending with the flour. Mix only until combined. Fold in the chopped walnuts.

Divide the batter evenly between the two prepared pans (about 445 grams in each pan) and smooth the tops with an offset spatula or the back of a spoon. Bake for about 20 minutes or until a toothpick inserted in the center comes out clean and the tops spring back when lightly pressed. Remove from oven and place on a wire rack to cool (in their pans) for about 10 minutes. Then, one cake at a time, place a wire rack on top of the cake pan and invert, lifting off the pan. Remove the parchment paper and then, to prevent cracks, reinvert the cakes onto a wire rack so that the tops are right side up. Cool completely before frosting.

Coffee Frosting: In the bowl of your electric stand mixer, fitted with the paddle attachment (or with a hand mixer), beat the mascarpone until smooth. Add the sugar, vanilla extract, and coffee mixture and beat until smooth and well blended. Scrape down the sides and bottom of your bowl. Add the cold whipping cream and, using the whisk attachment, beat the frosting until medium soft peaks form (frosting should be of spreading consistency). Do not over beat or the frosting will curdle.

Assemble: First remove about 1/2 cup (120 ml/grams) of the frosting and place in a piping bag fitted with a star tip (I used a Wilton 1M). Then place one cake layer, top of the cake facing down, onto your serving plate. Spread with half the frosting. Place the second cake layer on top of the frosting, top of the cake facing down, and cover the top of the cake with the remaining frosting. Then pipe swirls of frosting on the top of the cake. Place a walnut on each swirl of frosting.

Makes about 10-12 servings.

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