Cream softened butter and granulated sugar together until light and fluffy. Beat in the large eggs one at a time, ensuring each is fully incorporated before adding the next.

In a separate bowl, whisk together the all-purpose flour, baking powder, and salt. Gradually add the dry ingredients to the wet mixture, alternating with the whole milk and vanilla extract, mixing until just combined.

Pour the cake batter evenly into prepared baking pans and bake in a preheated oven until a toothpick inserted into the center comes out clean. Allow the cakes to cool completely on a wire rack before proceeding.

Once cooled, level the cake layers if necessary. Stack the layers, spreading a generous amount of white buttercream frosting between each layer and then crumb coating the entire cake.

Apply a final smooth layer of white buttercream frosting to the cake. Tint a portion of the remaining buttercream with red food coloring to create Santa's hat and other festive details.

Decorate the cake to resemble Santa Claus, using the red frosting for his hat and suit details, and white frosting for his beard and trim. Add white sprinkles for a snowy effect and place optional Santa hat decorations on top.