Preheat oven to 350º. Bake pecans in a single layer in a shallow pan 8 to 10 minutes or until toasted and fragrant, stirring halfway through.
Beat sugar and next 4 ingredients at high speed with a heavy-duty electric stand mixer 5 minutes. Stir together flour and next 4 ingredients; gradually add flour mixture to sugar mixture, beating at low speed just until blended. Add apples, chocolate, and pecans; beat just until blended. Spoon into 2 greased and floured 9-inch round cake pans.
Bake at 350º for 28 to 32 minutes or until a wooden pick inserted in center comes out clean. Cool in pans on a wire rack 10 minutes; remove from pans to wire rack, and cool completely (about 1 hour). Spread Browned Butter Frosting between layers and on top and sides of cake.
Mocha-Apple Bundt Cake: Omit Browned Butter Frosting. Prepare batter as directed; spoon into a greased and floured 12-cup Bundt pan. Bake at 350º for 1 hour to 1 hour and 10 minutes or until a long wooden pick inserted in center comes out clean. Cool in pan on a wire rack 15 minutes; remove from pan to wire rack, and cool completely (about 2 hours).