Preheat your oven to 350°F (175°C) and grease and flour two 9-inch round cake pans.

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

In a large mixing bowl, beat the softened butter and granulated sugar together until light and fluffy, about 3-4 minutes.

Add the eggs one at a time, mixing well after each addition, then stir in the vanilla extract.

Gradually add the dry ingredients to the butter mixture, alternating with the milk, starting and ending with the dry ingredients. Mix until just combined.

Divide the batter evenly between the two prepared cake pans and smooth the tops.

Bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean. Let cool in the pans for 10 minutes, then transfer to a wire rack to cool completely.

While the cakes cool, prepare the frosting by beating the softened butter until creamy, then gradually add the powdered sugar and milk, mixing until fluffy.

Once the cakes are completely cool, layer them on a serving plate, spreading frosting between the layers and on the top and sides of the cake.

Decorate with Capricorn-themed decorations, edible glitter, or sprinkles as desired.