Preheat your oven to 350°F (175°C). Grease and line two 8-inch round cake pans. In a bowl, whisk together flour, baking powder, and salt. In a large mixing bowl, cream the butter and sugar until fluffy. Beat in the eggs one at a time, then stir in vanilla extract.
Add the flour mixture in three parts, alternating with the buttermilk, beginning and ending with the flour. Mix until just combined. Divide the batter evenly between the pans and smooth the tops. Bake for 30–35 minutes or until a toothpick comes out clean.
Let the cakes cool in the pans for 10 minutes, then turn out onto wire racks to cool completely. For the frosting, beat the butter until creamy. Add powdered sugar gradually, then mix in vanilla, salt, and enough cream to reach your desired consistency.
Once cakes are cool, level the tops if needed. Spread frosting over one layer, add the second, and frost the top and sides. Decorate with sprinkles, piped borders, or candles as desired.