First Step: Prep and Preheat
Preheat your oven to 325°F (162°C). Grease and flour three 9-inch cake pans, lining the bottoms with parchment paper circles to avoid sticking and ensure easy removal.

Second Step: Mix Cake Batter
In a large mixing bowl, combine the two white cake mixes with vanilla yogurt, water, egg whites, and oil. Mix initially on low speed for 30 seconds to incorporate dry ingredients, then beat on medium-high for 2 minutes until the batter thickens and becomes smooth.

Third Step: Divide and Color Batter
Divide the batter evenly into three separate bowls. Use gel food coloring to tint each portion in desired pastel shades such as lemon yellow, teal, and pink, blending until color is uniform and vibrant.

Fourth Step: Bake Layers
Distribute each colored batter evenly into the prepared pans. Gently tap pans to release air bubbles and smooth tops. Bake for 35 to 45 minutes, testing doneness with a toothpick which should come out clean when inserted into the center.

Fifth Step: Cool and Level
Allow cakes to cool in their pans for about 30 minutes. Carefully remove cakes onto wire racks, peel off parchment paper, and cool completely. Use a serrated knife to trim rounded tops evenly, reserving trimmed crumbs for decoration.

Sixth Step: Make Frosting
Beat softened cream cheese in a bowl until smooth. Add powdered sugar gradually and mix well. Blend in marshmallow cream and vanilla bean paste, smoothing the mixture. Finally, gently fold in thawed whipped topping to create a light, fluffy frosting texture.

Seventh Step: Assemble the Cake
Place one cake layer on a serving plate. Spread approximately 1 cup of frosting over it. Repeat with the second layer and frosting. Stack the final layer and cover the entire cake with the remaining frosting.

Eighth Step: Decorate
Use an offset spatula to create rustic ruffles on the cake’s sides and top by turning the cake slowly while pressing the spatula upward and outward. Sprinkle the reserved pastel cake crumbs evenly on top for a festive, spring-like finish.

Final Step: Serve and Enjoy
Serve the cake the same day if possible, storing uncovered in the refrigerator. For leftovers, cover loosely with plastic wrap and refrigerate for 2-3 days, or freeze tightly wrapped for up to 4 weeks, thawing overnight before serving.