Marble Cake

Preheat the oven to 375°F (190°C).

Grease your cake pan generously with butter. A 9x5-inch loaf pan, 9x9 or 8x8-inch square pan, or a round pan all work.

Mix the flour and baking powder together, then sift.

Add the salt to the flour mixture, mix well, and set aside.

Using a hand mixer or stand mixer, beat the butter and sugar until pale yellow and well combined.

Add the first egg and beat until creamy, scraping down the sides.

Add the remaining eggs one at a time, beating well after each addition until creamy.

Add the vanilla extract and mix well.

Fold the sifted flour mixture into the batter and mix well.

Add the milk and mix into a smooth batter.

Divide the batter into two equal portions.

Stir the cocoa powder into one portion until well combined to make the chocolate batter.

Transfer the plain batter into the greased pan and shake it lightly to level it.

Pour the cocoa batter into the middle of the pan.

Lightly swirl the two batters together with a butter knife, drawing an "S" shape a few times. Be careful not to overmix.

Bake until golden brown and cooked through, about 40 minutes.

If the top browns too quickly before the cake sets, cover it with aluminum foil at the 20-minute mark.

Insert a cake tester into the center to check doneness; if the middle is still wet, bake a little longer.

Remove from the oven and let cool on a wire rack for 5 minutes, then turn out of the pan, slice, and serve.