Preheat your oven to 350°F (175°C). Grease and flour two 8-inch round cake pans.

In a large bowl, cream together the butter and sugar until light and fluffy. Add the eggs, one at a time, beating well after each addition. Mix in the vanilla extract.

In a separate bowl, whisk together the flour, baking powder, and salt. Gradually add the dry ingredients to the wet ingredients, alternating with milk. Mix until just combined.

Divide the batter evenly between the prepared cake pans. Bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean. Let the cakes cool in the pans for 10 minutes, then transfer them to a wire rack to cool completely.

In a large bowl, beat the softened butter until smooth. Gradually add powdered sugar, 1 cup at a time, beating until smooth. Add heavy cream, vanilla extract, and a pinch of salt, and beat until the frosting is light and fluffy.

Once the cakes are completely cooled, place one cake layer on a cake board or plate. Spread a layer of frosting over the top. Place the second cake layer on top and frost the entire cake with a smooth layer of buttercream.

Roll out fondant and use it to create a graduation cap, rolled-up diploma, or any other design elements you like. Use gel food coloring to match the cake to the school's colors. Decorate the top and sides with the fondant pieces, piping gel, or extra frosting for details.

Add any final decorative touches, like edible gold or silver sprinkles. Let the cake set for about 30 minutes before serving to allow the decorations to firm up.