1-First Step: Prepare the dough baseCream 1 cup softened butter with 2 cups sugar in a large bowl using a mixer on medium speed for 2-3 minutes until light and fluffy. Add 4 eggs one at a time, beating well after each. Mix in 1 tsp vanilla extract. In a separate bowl, whisk 5 cups flour, 1 tsp baking powder, and ½ tsp salt. Gradually add dry ingredients to wet on low speed until just combined. Dough will be sticky; chill 30 minutes if needed for easier handling. This step takes 10 minutes and sets chewy texture.

2-Second Step: Spread and bakeGrease a 15×10-inch jelly roll pan thoroughly or line with parchment. Spread dough evenly using wet spatula or greased hands, aiming for uniform ¼-inch thickness. Edges may be higher; press down gently. Bake at 375°F for 18-22 minutes. Watch for golden edges and set center; toothpick should come out clean. Avoid overbaking for softness. Cool in pan on wire rack 1 hour or until room temperature. Baking time: 20 minutes.

3-Third Step: Make the frostingBeat ½ cup room-temperature butter until creamy, about 1 minute. Sift in 4 cups powdered sugar gradually, mixing on low to avoid clouds. Add 1 tsp vanilla and 2-4 tbsp milk until spreadable. Divide into bowls for colors; tint with gel food coloring drops for desired shades. Whip 1-2 minutes for fluffiness. This buttercream pipes well or spreads smoothly, taking 5 minutes.

4-Fourth Step: Frost and decorateOnce bars fully cool, spread frosting evenly, about ¼-inch thick. Use offset spatula for clean edges. Pipe rosettes if desired. Sprinkle generously while wet for adhesion. Chill 15 minutes to set. This adds party flair in 10 minutes.

5-Final Step: Cut and serveRun knife around edges, then cut into 24-36 squares. Serve on platter. Store as noted below. Total prep shines for events.