Step 1: Prepare the Cake Batter

1. Preheat the Oven: Preheat your oven to 350°F (175°C). Grease and flour a 9-inch loaf pan or two 8-inch round cake pans. Line the bottom with parchment paper for easier release.
2. Cream the Butter and Sugar: In a large mixing bowl, beat the softened butter and granulated sugar until light and fluffy, about 3-5 minutes using a hand mixer or stand mixer on medium speed. Scrape down the sides of the bowl as needed.
3. Incorporate the Eggs: Add the eggs one at a time, beating well after each addition. This ensures a smooth and emulsified mixture.
4. Mix Dry Ingredients: In a separate bowl, sift together the all-purpose flour, baking powder, and salt. This step prevents clumps and ensures even mixing.

Step 2: Combine Wet and Dry Ingredients

5. Alternate Flour and Milk: With the mixer on low, gradually add the dry flour mixture to the creamed butter, alternating with the milk. Start and end with the flour mixture. Mix until just combined. Avoid overmixing to keep the cake tender.
6. Add Vanilla Extract: Stir in the vanilla extract, ensuring the batter is smooth.

Step 3: Prepare the Chocolate Batter

7. Mix Cocoa Paste: In a small bowl, combine the cocoa powder with boiling water to create a smooth, thick paste. Cool slightly.
8. Divide the Batter: Separate ⅓ of the vanilla cake batter into another bowl and fold in the cocoa paste until well blended. You should have one portion of vanilla batter and one portion of chocolate batter.

Step 4: Create the Marble Effect

9. Layer the Batter: Spoon alternating dollops of vanilla and chocolate batter into the prepared pan. Use a butter knife to swirl the batters together gently, creating a marbled effect. Do not over-swirl, or you’ll lose the marbled design.
10. Bake the Cake: Bake for 45-55 minutes, or until a toothpick inserted into the center comes out clean. Cool the cake in the pan for 10 minutes, then turn it out onto a wire rack to cool completely.

Step 5: Make the Almond Vanilla Glaze

11. Prepare the Glaze: In a medium bowl, whisk together powdered sugar, heavy cream, vanilla extract, and almond extract until smooth and pourable. Adjust the consistency by adding more cream if needed.
12. Drizzle and Decorate: Once the cake has cooled, drizzle the glaze over the top. Sprinkle sliced almonds over the glaze for added texture and flavor.