Step 1: Bake the Cake

1. Preheat oven to 350°F (175°C). Grease and line a 9×13-inch baking pan with parchment paper.
2. In a bowl, whisk together flour, baking powder, and salt. Set aside.
3. In a large mixing bowl, beat butter and sugar until light and fluffy (about 2-3 minutes).
4. Add eggs one at a time, beating well after each. Mix in vanilla extract.
5. Gradually add the dry ingredients, alternating with milk, starting and ending with dry ingredients. Mix until just combined.
6. Pour batter into the prepared baking pan and spread evenly.
7. Bake for 18-22 minutes, or until a toothpick inserted in the center comes out clean.
8. Let the cake cool completely before cutting.

Step 2: Make the Buttercream Frosting

1. In a large bowl, beat butter until smooth.
2. Add powdered sugar, one cup at a time, mixing on low.
3. Pour in heavy cream, vanilla extract, and salt. Beat until smooth and fluffy.
4. If using food coloring, divide the frosting and mix in desired colors.

Step 3: Assemble the Mini Cakes

1. Once the cake is cool, use a 3 to 4-inch round cookie cutter to cut out small cake layers.
2. Place one cake round on a parchment-lined surface. Spread a thin layer of frosting on top.
3. Add a second cake round and repeat the frosting layer.
4. Apply a crumb coat (a thin layer of frosting) and chill for 15 minutes.
5. Frost the entire cake smoothly and decorate as desired.

Step 4: Decorate & Package

1. Pipe designs or write messages using colored buttercream.
2. Place the mini cake in a small takeout box lined with parchment paper or a doily.
3. Refrigerate for 30 minutes before serving.