Preheat your oven to 350°F (175°C). Grease and flour an 8x8 inch square baking pan or a 9-inch round pan.

In a large mixing bowl, whisk together the flour, granulated sugar, baking powder, and salt for the red heart cake.

Add the softened butter, eggs, whole milk, and vanilla extract to the dry ingredients. Beat with an electric mixer until the batter is smooth.

Stir in the red food coloring until you achieve a vibrant red color. Pour the batter into the prepared pan and bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean.

Allow the red cake to cool completely on a wire rack before proceeding. Once cooled, carefully remove it from the pan.

Using a heart-shaped cookie cutter (about 2-3 inches wide), cut out as many heart shapes as possible from the red cake. Set these hearts aside.

Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.

In a large mixing bowl, whisk together the flour, granulated sugar, baking powder, and salt for the main vanilla cake.

Add the softened butter, eggs, whole milk, and vanilla extract to the dry ingredients. Beat with an electric mixer until the batter is smooth.

Pour about one-third of the main vanilla cake batter into the bottom of one of the prepared 9-inch pans.

Arrange the red heart cut-outs upright in a single row down the center of the pan, making sure they are close together. They should stand tall.

Carefully pour the remaining main vanilla cake batter over and around the hearts, ensuring they remain upright and are fully covered. Repeat this process if you are making a second layer in the other pan.

Bake for 30-35 minutes, or until a toothpick inserted into the vanilla cake (avoiding the red heart) comes out clean.

Let the cakes cool in their pans for 10 minutes, then invert them onto a wire rack to cool completely before frosting.

In a large bowl, beat the softened unsalted butter until creamy for the buttercream frosting.

Gradually add the powdered sugar, mixing until combined. Then, add the vanilla extract and 2 tablespoons of heavy cream or milk. Beat until the frosting is light and fluffy, adding more liquid a tablespoon at a time if needed to reach your desired consistency.

Once the cakes are completely cool, level them with a serrated knife if necessary to create flat tops.

Place one cake layer on your serving plate or cake stand. Spread an even layer of buttercream frosting on top. If making a two-layer cake, carefully place the second cake layer on top.

Frost the top and sides of the entire cake with the remaining buttercream. Decorate as desired.