Preheat your oven to 350°F (175°C). Grease and flour a 9-inch round cake pan or line it with parchment paper.

Whisk together the flour, baking powder, and salt in a medium bowl.

Cream the softened butter and granulated sugar in a large mixing bowl until light and fluffy, about 3-4 minutes.

Add the eggs one at a time, followed by the vanilla extract and orange zest, mixing well after each addition.

Combine the dry ingredients with the butter mixture, alternating with the milk. Mix until just incorporated.

Mix the cocoa powder with boiling water in a separate bowl until smooth. Then fold half of the cake batter into the cocoa mixture.

Spoon alternating dollops of the vanilla batter and chocolate batter into the prepared cake pan. Use a knife or skewer to swirl the batters together.

Bake for 30–35 minutes, or until a toothpick inserted comes out clean. Cool in the pan for about 10 minutes before transferring to a wire rack.

Whisk together the powdered sugar and enough orange juice to achieve a smooth consistency for the glaze.

Drizzle the orange glaze over the cooled cake, letting it drip down the sides.

Sprinkle with additional orange zest for garnish.

Slice and serve with friends and family, or enjoy it all by yourself!