Let’s tackle this exciting cake project component by component:

1. Make the Cake Layers:

Preheat oven to 340°F (171°C). Butter and flour three 6-inch round cake pans. Line bottoms with parchment paper. Wrap pans with cake strips (if using).

Sift together flour, baking powder, baking soda, and salt in a large bowl.

In a separate medium bowl, whisk together the room temperature egg whites, vanilla extract, sour cream, and milk. (Self-correction: Recipe mixes oil with wet, but no oil listed – assuming it meant beat egg whites separately? Re-reading: No oil listed. Okay, whisking whites with vanilla/sour/milk is unusual but following recipe.)

In the bowl of a stand mixer, cream the room temperature butter and granulated sugar until light and fluffy.

Add the wet ingredients (egg white/milk/sour cream/vanilla mix) to the dry ingredients. Mix on low speed until just combined. (Self-correction: This seems wrong based on standard methods & the creaming step. Standard method would be cream butter/sugar, add eggs/whites+vanilla, then alternate dry and milk/sour cream. Let’s adjust to standard method for clarity)

Revised Cake Steps (Standard Method):

• (Prep) Preheat 340°F, prep 3×6″ pans. Sift dry ingredients (flour, baking powder, soda, salt). Whisk wet (sour cream, milk, vanilla).
• (Cream) In stand mixer, beat room temp butter and sugar until light/fluffy (3-5 mins).
• (Add Eggs/Whites) Beat in room temp egg whites one at a time. Beat in vanilla.
• (Alternate) On low speed, add ⅓ dry ingredients, mix briefly. Add ½ wet ingredients, mix briefly. Repeat (⅓ dry, remaining wet, remaining dry), mixing just until combined after each.
• (Sprinkles) Gently fold in sprinkles.
• (Bake) Divide batter into pans. Bake 30-35 mins until toothpick is clean. Cool 10 mins in pans, then invert onto racks to cool completely.

2. Make the Italian Meringue Buttercream (IMBC):

In a stand mixer bowl (clean!), beat room temp egg whites, cream of tartar, salt, and ⅓ cup sugar with the whisk attachment until soft peaks form.

In a medium saucepan, combine the remaining 1 cup sugar and ⅓ cup water. Place over low heat, stirring constantly until sugar dissolves and syrup is clear.

Increase heat to medium-high. Attach a candy thermometer. Boil syrup without stirring until it reaches 235-240°F (113-115°C – soft-ball stage).

Immediately remove syrup from heat. With the mixer running on medium-low speed, very slowly drizzle the hot syrup down the side of the bowl into the whipping egg whites. Avoid hitting the whisk.

Once all syrup is added, increase speed to high and beat until the meringue is stiff, glossy, and the bottom of the bowl feels cool to the touch (about 7-10 minutes).

Switch to the paddle attachment. With the mixer on medium-low speed, add the room temperature butter, one cube at a time, beating until incorporated. The mixture may look curdled – keep beating! It will come together.

Once all butter is added, beat on medium-high until silky smooth. Beat in the vanilla extract. Set aside (can be stored airtight).

3. Make the Funfetti American Buttercream (ABC):

Beat the room temperature butter in a stand mixer (or large bowl) until light and fluffy.

Gradually add the sifted confectioners’ sugar and salt, mixing on low speed until combined.

Add the milk and vanilla extract. Increase speed to medium-high and beat for several minutes until very light and fluffy.

Divide the frosting into two batches. Add pink food coloring to one batch and mix until desired color. Fold sprinkles into both batches.

4. Prepare Piping Bags for Crumb Coat:

Transfer frosting into 4 piping bags (2 pink, 2 white). Place one pink bag and one white bag together inside a larger piping bag fitted with a large round or plain tip (or just snip the end off the larger bag). This setup allows piping alternating colors for the crumb coat. (Self-correction: Directions say snip tip off combined bag, implying no metal tip needed for this stage).

5. Make the Ganache:

Chop candy melts (if large). Place candy melts and white chocolate chips in a microwave-safe bowl.

Add heavy cream. Microwave on medium power (50%) in 20-30 second intervals, stirring well after each, until melted and smooth. Do not overheat.

Add a drop of pink food coloring, if desired, and whisk until smooth. Let cool slightly until thickened but still pourable. Transfer to a piping bag or squeeze bottle.

6. Assemble the Cake:

Level the cooled cake layers if needed. Place one layer on a cake stand or board.

Pipe alternating pink and white ABC using the combined piping bag setup around the edge of the first layer to create a dam. Fill the center with dollops of pink/white ABC (or use the individual bags). Spread slightly. (Self-correction: Directions say pipe pink/white buttercream between layers – implying use ABC for filling too). Okay, using ABC for filling.

Place the second cake layer on top. Repeat piping/filling with ABC. Place the third cake layer on top.

Apply a “crumb coat” using the alternating pink/white ABC piping bag setup around the sides of the cake. Smooth lightly with an offset spatula or bench scraper – it doesn’t need to be perfect. Chill the cake for about 10 minutes to firm up the crumb coat.

7. Final Frosting (IMBC):

Cover the entire cake (top and sides) with the prepared Italian Meringue Buttercream. Use an offset spatula and bench scraper to get a smooth finish.

Chill the cake again for another 10 minutes to firm the frosting.

8. Add Sprinkle Skirt:

Gently press confetti sprinkles onto the bottom 1-2 inches of the frosted cake to create a “skirt.”

9. Ganache Drip:

Carefully apply the slightly cooled pink ganache around the top edge of the chilled cake, letting it drip down the sides. Smooth the ganache on the very top surface if desired. Let the ganache cool and set slightly.

10. Final Piping:

Transfer remaining IMBC to a piping bag fitted with a large star tip (like #869). Pipe decorative dollops or swirls around the top edge of the cake, on top of the set ganache.

11. Chill and Serve:

Chill the finished cake for at least 30 minutes to allow everything to set before slicing and serving. Let sit at room temperature for 15-20 minutes before serving for best texture