We like the way this cake looks glazed with white chocolate, but you can substitute semisweet chocolate in the glaze recipe, if you prefer. Be careful not to over swirl the vanilla and chocolate batters when you are running a knife through the two; the marbling won’t look as beautiful if you overdo it.

　　

Ingredients

makes one 9-by-5-inch loaf

　　1 stick (1/2 cup) unsalted butter, room temperature, plus more for pan

　　1 3/4 cups cake flour (not self-rising)

　　2 teaspoons baking powder

　　1/2 teaspoon salt

　　1 cup sugar

　　3 large eggs, room temperature

　　1 teaspoon pure vanilla extract

　　2/3 cup buttermilk, room temperature

　　1/4 cup plus 1 tablespoon Dutch-process cocoa powder

　　1/4 cup plus 2 tablespoons boiling water

　　White-Chocolate Glaze (recipe follows)

　　

White-Chocolate Glaze

3/4 cup confectioners’ sugar, sifted, plus more if needed

　　2 tablespoons milk, plus more if needed

　　2 1/4 ounces best-quality white chocolate, melted and cooled

　　(makes enough for one 9-by-5-inch loaf)

　　

Step 1

Preheat the oven to 350°F. Generously butter a 9-by-5-inch loaf pan; set aside. Whisk together the cake flour, baking powder, and salt; set aside.

　　

Step 2

In the bowl of an electric mixer fitted with the paddle attachment, beat the butter and sugar until light and fluffy, about 5 minutes. Add the eggs one at a time, beating until combined after each addition and scraping down the sides of the bowl as needed. Mix in the vanilla. Add the flour mixture in two batches, alternating with the buttermilk and beginning and ending with the flour. Set aside one-third of the batter.

　　

Step 3

In a bowl, mix the cocoa and the boiling water with a rubber spatula until smooth. Add the cocoa mixture to the reserved cake batter; stir until well combined.

　　

Step 4

Spoon the batters into the prepared pan in two layers, alternating spoonfuls of vanilla and chocolate to simulate a checkerboard. To create marbling, run a table knife (or wooden skewer) through the batters in a swirling motion.

　　

Step 5

Bake, rotating the pan halfway through, until a cake tester comes out clean, 40 to 50 minutes. Transfer pan to a rack to cool 10 minutes. Turn out cake from the pan and cool completely on the rack. Pour glaze over cake, letting it drip down the sides. Cake can be kept in an airtight container at room temperature for up to 3 days.

　　

White-Chocolate Glaze

Step 6

In a small bowl, whisk together the confectioners’ sugar and milk.The mixture should have the consistency of thin sour cream. Add the melted chocolate and whisk until glaze is smooth. If it is too thin, add more sugar, 1 tablespoon at a time; if too thick, add more milk, 1 teaspoon at a time. Use immediately.

　　

Marbleizing how-to

Step 7

Spoonfuls of vanilla and chocolate batters are alternated, in two layers, in a checkerboard pattern.

　　

Step 8

A table knife is run through the batters to create swirls.

　　Reprinted with permission from Martha Stewart's Baking Handbook by Martha Stewart. © 2005 Clarkson Potter