Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans or line them with parchment paper.

In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.

In a large mixing bowl, beat the softened butter and granulated sugar together on medium-high speed until pale and fluffy, about 3-5 minutes.

Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract.

With the mixer on low speed, add the flour mixture in three parts, alternating with the buttermilk in two parts. Start and end with flour. Mix until just combined.

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

In a large bowl, beat the butter until creamy. Gradually add the sifted powdered sugar, mixing well on medium speed.

Add the vanilla extract and a pinch of salt. Add cream or milk one tablespoon at a time until you reach your desired consistency. Beat until fluffy—about 3-5 minutes.

Place one cake layer on a serving plate. Spread a generous layer of frosting on top. Place the second cake layer over it, then frost the top and sides.