Coffee Walnut Cake2017-12-30
Position rack in center of oven and preheat to 350°F. Butter and flour two 9-inch-diameter cake pans with 1 1/2-inch-high sides. Blend 1/2 cup walnuts, 1 tablespoon sugar, and espresso in processor until nuts are finely ground. Whisk flour, baking powder, cinnamon, baking soda, and salt in medium bowl to blend. Using electric mixer, beat butter in large bowl until smooth. Gradually add remaining sugar (1 cup minus 1 tablespoon), beating until fluffy. Beat in eggs, 1 at a time, then egg yolk. Add ground walnut mixture and vanilla; beat to blend. Reduce mixer speed to low and beat in dry ingredients in 3 additions alternately with buttermilk in 2 additions. Fold in remaining 1/2 cup walnuts. Divide batter evenly between prepared pans. Bake cake layers until tester inserted into center comes out clean, about 26 minutes. Cool in pans 5 minutes, then turn out onto racks and cool completely. Stir espresso and 1 tablespoon water in large bowl until coffee dissolves. Add cream, mascarpone, sugar, and vanilla. Beat until filling is thick and smooth (do not overbeat or filling may curdle). Place 1 cake layer on platter, flat side up. Spread half of filling over cake. Place second layer, flat side down, on filling. Spread remaining filling over top. Mix walnuts, cinnamon, and salt. Sprinkle over top of cake. Cover with cake dome. Chill at least 1 hour and up to 1 day.