Step 1: Prepare the Cake Batter

1. Preheat oven to 350°F (175°C). Grease and line two 9-inch round cake pans with parchment paper.
2. In a bowl, whisk together flour, baking powder, baking soda, and salt. Set aside.
3. In a large mixing bowl, beat butter and sugar until light and fluffy.
4. Add eggs one at a time, beating well after each. Stir in vanilla extract.
5. Alternately add dry ingredients and milk, mixing until just combined.
6. Fold in sour cream for extra moisture.

Step 2: Bake the Cake

1. Divide the batter evenly between the two cake pans.
2. Bake for 30-35 minutes or until a toothpick inserted in the center comes out clean.
3. Let cakes cool in pans for 10 minutes, then transfer to a wire rack to cool completely.

Step 3: Make the Buttercream Frosting

1. In a bowl, beat butter until smooth and creamy.
2. Gradually add powdered sugar, mixing well.
3. Stir in vanilla extract and salt.
4. Add heavy cream and beat until frosting is fluffy.

Step 4: Assemble & Frost the Cake

1. Level the cake layers by trimming the tops if needed.
2. Place one cake layer on a plate and spread frosting evenly over the top.
3. Add the second layer and frost the entire cake.
4. Use a spatula to smooth out the frosting.

Step 5: Decorate & Serve

1. Add sprinkles, edible glitter, or fresh fruits for decoration.
2. Place birthday candles on top.
3. Slice, serve, and celebrate! 🎉🎂