01 - Preheat oven to 350°F. Grease and flour two 9-inch round cake pans, lining bottoms with parchment paper.
02 - In a medium bowl, whisk together flour, baking powder, and salt until well combined.
03 - Beat butter and sugar with an electric mixer until light and fluffy, approximately 3 minutes.
04 - Add eggs one at a time, mixing thoroughly after each addition. Stir in vanilla extract.
05 - Add flour mixture in three additions, alternating with milk, beginning and ending with flour. Mix just until combined.
06 - Divide batter evenly between prepared pans. Bake for 30-35 minutes, or until a toothpick inserted into center comes out clean.
07 - Cool cakes in pans for 10 minutes, then turn out onto wire racks to cool completely.
08 - Beat butter until creamy. Gradually add powdered sugar, mixing until smooth. Mix in vanilla and salt.
09 - Add milk 1 tablespoon at a time until reaching spreadable consistency.
10 - Divide icing into three bowls. Tint one bowl purple, one green, and one gold using gel food coloring. Mix each until evenly colored.
11 - Place one cake layer on serving platter. Spread a thin layer of any icing color over top. Place second cake layer on top.
12 - Frost the cake with tricolor stripes or swirls, alternating purple, green, and gold icing around sides and top using an offset spatula.
13 - Sprinkle with colored sugars or edible glitter in Mardi Gras shades for extra flair.