Preheat oven to 350 degrees. Butter pans; line with parchment paper. Butter lining; dust with flour, tapping out excess. Set aside. Sift together cake flour, baking powder, and salt; set aside.Advertisement
Combine milk and cream in a small bowl; set aside. Cream butter and sugar on medium speed in the bowl of an electric mixer fitted with the whisk until pale and fluffy, about 5 minutes. Add eggs one at a time; mix well after each addition. Mix in vanilla. Add flour mixture in three batches, alternating with the milk mixture and beginning and ending with flour.
Combine cocoa and the boiling water in a medium bowl; for mocha cake, add espresso powder. Stir in 1 cup cake batter.
Fill prepared pans with spoonfuls of vanilla and chocolate batter to form a checkerboard pattern. Run the tip of a paring knife or a wooden skewer through batter in a figure-eight motion to make swirls. Bake until tops are golden, and a cake tester inserted in centers comes out clean, 40 to 50 minutes. Let cakes cool completely in pans on wire racks.