Step 1: Prepare the Oven and Cake Pan

1. Preheat your oven to 350°F (175°C). Grease and flour a 9-inch bundt pan or two 9-inch round cake pans. Ensure the pans are evenly coated to prevent sticking.

Step 2: Mix the Dry Ingredients

2. In a medium-sized bowl, sift together the flour, baking powder, baking soda, and salt. Set aside for later.

Step 3: Cream the Butter and Sugar

3. In a large mixing bowl, use an electric mixer to cream the butter and granulated sugar until light and fluffy—about 3-5 minutes. The mixture should be pale and airy. This step helps incorporate air into the batter, ensuring a fluffy cake.

Step 4: Add the Eggs and Vanilla

4. Beat in the eggs one at a time, ensuring each egg is fully incorporated before adding the next. Add the vanilla extract and continue to mix until well combined.

Step 5: Combine the Dry and Wet Ingredients

5. Gradually add the sifted dry ingredients to the butter mixture, alternating with the milk. Start and end with the dry ingredients, mixing gently until the batter is smooth and just combined. Be careful not to overmix, as this can make the cake dense.

Step 6: Prepare the Chocolate Batter

6. In a small bowl, mix the cocoa powder, hot water, and instant coffee powder until smooth. Take about 1 ½ cups of the vanilla batter and blend it with the chocolate mixture until fully combined.

Step 7: Create the Marble Effect

7. Spoon the vanilla and chocolate batters into the prepared pan alternately. To achieve a marbled pattern, use a knife or skewer to swirl the batters together gently. Avoid over-mixing to keep the distinct patterns visible.

Step 8: Bake the Cake

8. Bake in the preheated oven for 45-55 minutes, or until a toothpick inserted into the center comes out clean. If baking in round pans, check for doneness after 30-35 minutes. Cool the cake in the pan for 10 minutes before transferring to a wire rack to cool completely.

Step 9: Prepare the Vanilla-Chocolate Swirl Glaze

9. In a medium bowl, whisk together powdered sugar, melted butter, and 3 tablespoons of milk until smooth. Add the vanilla extract and mix well. Divide the glaze into two equal portions. In one portion, add cocoa powder and 1 tablespoon of hot water, mixing until smooth. If either glaze is too thick, add more milk 1 teaspoon at a time until it reaches your desired consistency.

Step 10: Glaze the Cake

10. Drizzle the vanilla glaze over the cooled cake, then follow with the chocolate glaze, allowing both to drip down the sides naturally. Use a toothpick to swirl the two glazes together gently for a marbled effect