Preheat the oven to 350°F. Grease two 8-inch round cake pans, line with parchment, and cream the butter and sugar until pale and fluffy, about 3 minutes.

Beat in the eggs one at a time, then add the vanilla extract and beat until combined.

Whisk together the flour, baking powder, and salt. Add the dry ingredients to the batter in three additions, alternating with buttermilk and mixing just until smooth.

Divide the batter between the pans and bake for 25 to 30 minutes, until a toothpick comes out clean. Cool in the pans for 10 minutes, then turn out to cool completely.

For the buttercream, beat the butter until creamy, then gradually add the powdered sugar, cream, and vanilla. Whip on medium-high until light and fluffy.

Place one cake layer on a plate, spread with buttercream, top with the second layer, and frost the entire cake. Chill briefly to set, then finish with a final swirl.