01 - Preheat oven to 350°F. Grease and flour two 9-inch round cake pans, lining bottoms with parchment paper.
02 - Whisk together flour, baking powder, and salt in a medium bowl until evenly distributed.
03 - Beat butter and sugar with electric mixer on medium-high speed until light and fluffy, approximately 3 minutes.
04 - Add eggs one at a time, mixing thoroughly after each addition. Blend in vanilla extract.
05 - Add flour mixture in three additions, alternating with milk, beginning and ending with flour. Mix until just combined, being careful not to overmix.
06 - Divide batter evenly between prepared pans, smoothing tops. Bake for 30–35 minutes or until toothpick inserted in center comes out clean.
07 - Let cakes cool in pans for 10 minutes, then invert onto wire racks to cool completely before frosting.
08 - Beat butter until creamy. Gradually incorporate powdered sugar until smooth. Mix in vanilla and salt.
09 - Add milk one tablespoon at a time until spreadable consistency is achieved.
10 - Divide icing among three bowls. Tint each bowl with purple, green, or gold gel food coloring, mixing until uniform color develops.
11 - Place first cake layer on serving platter. Spread thin layer of any colored icing over top. Position second layer atop frosting.
12 - Frost cake exterior with alternating purple, green, and gold stripes or swirls using offset spatula. Create decorative patterns as desired.
13 - Sprinkle with colored sugars or edible glitter in Mardi Gras shades for enhanced presentation.