Step 1: Prepare the Sponge Cake

1. Preheat oven to 350°F (175°C). Grease and line two 9-inch cake pans.
2. In a bowl, sift together flour, baking powder, and salt. Set aside.
3. In another bowl, beat butter and sugar until fluffy (about 3 minutes).
4. Add eggs one at a time, beating well after each. Stir in vanilla extract.
5. Gradually add the dry ingredients and milk, alternating, starting and ending with flour.
6. Divide batter evenly between pans and bake for 30-35 minutes until a toothpick comes out clean.
7. Cool completely before decorating.

Step 2: Make the Buttercream Frosting

1. Beat butter until creamy (about 2 minutes).
2. Slowly add powdered sugar, mixing until smooth.
3. Add heavy cream and vanilla extract, and beat for another 2-3 minutes until fluffy.
4. If making house-themed cakes, divide the frosting and color with red, green, blue, or yellow.

Step 3: Assemble & Decorate

1. Place one cake layer on a serving plate, spread frosting evenly, and top with the second layer.
2. Frost the outside smoothly, or pipe house-colored designs.
3. Use fondant to create decorations, such as a scar, glasses, house banners, or a spellbook.
4. For a golden snitch: Roll gold fondant into a ball and attach sugar-paper wings.
5. For a chocolate wand: Melt chocolate, pipe onto wax paper, and let harden.
6. Dust with edible gold dust for a magical effect!