Prepare the Cake

1. Preheat Oven: Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans, or line them with parchment paper for easy removal.
2. Mix Dry Ingredients: In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.
3. Cream Butter and Sugar: In a large bowl, cream together the softened butter and sugar until light and fluffy, about 3-4 minutes.
4. Add Eggs and Vanilla: Add the eggs, one at a time, beating well after each addition. Stir in the vanilla extract.
5. Alternate Adding Dry Ingredients and Wet Ingredients: Gradually add the dry ingredients to the butter mixture in three parts, alternating with the sour cream and milk. Start and end with the dry ingredients. Mix until just combined.
6. Color the Batter: Divide the batter evenly into two bowls. Add the red food coloring to one bowl and mix until you achieve your desired shade of red.
7. Layer the Batter: Spoon dollops of the plain and red batter into the center of each cake pan. Continue alternating the two colors until all batter is added. Use a skewer or knife to swirl the colors together, creating a marbled effect.
8. Bake: Bake in the preheated oven for 30-35 minutes or until a toothpick inserted into the center comes out clean.
9. Cool: Let the cakes cool in the pans for 10 minutes before transferring them to wire racks to cool completely.

Prepare the Cream Cheese Frosting

1. Cream the Butter and Cream Cheese: Beat the softened butter and cream cheese together in a large bowl until smooth and fluffy.
2. Add Powdered Sugar: Gradually add powdered sugar, 1 cup at a time, mixing well after each addition until the frosting is smooth.
3. Flavor and Adjust Consistency: Stir in the vanilla extract. Add milk, one tablespoon at a time, to reach your desired frosting consistency.
4. Color the Frosting: Divide the frosting into two bowls. Add pink food coloring to one bowl and red food coloring to the other, mixing until the colors are well incorporated.

Assemble the Cake

1. Layer the Cake: Place one of the cooled cake layers on a cake stand or serving platter. Spread a layer of pink frosting over the top.
2. Add the Second Layer: Place the second cake layer on top of the frosting. Apply a crumb coat (a thin layer of frosting) to seal in the crumbs.
3. Frost the Cake: Once the crumb coat is set, use a piping bag or spatula to apply the red and pink frosting. Swirl the colors together for a beautiful, marbled effect.
4. Decorate: Add any additional decorations such as heart-shaped sprinkles, edible glitter, or even a drizzle of chocolate syrup to make your cake extra special.