Preheat your oven to 325 degrees F. Spray three 8-inch pans with non-stick cooking spray, line the bottoms with parchment and spray again. Set aside.

Place the pretzel sticks in a food processor or blender and pulse until the pretzels are finely ground and resemble flour. When you remeasure, you should have about a cup.

In a medium-size bowl, combine the pretzel crumbs, all-purpose flour, baking powder, baking soda, and salt. Whisk until the ingredients are well-blended.

In the bowl of a stand mixer fitted the paddle attachment, beat the butter and sugars on medium speed until light and fluffy. Add the eggs, one at a time, beating well after each addition.

With the mixer on low speed, add 1/3 of the dry ingredients and mix until combined. Slowly add half of the buttermilk and mix until incorporated. Continue alternating the flour and buttermilk until it has all been incorporated. Scrape down the sides of the bowl and slowly mix for another 20-30 seconds.

Divide the batter evenly among your pans and bake for about 25 to 30 minutes. Cool 10 minutes on a wire rack before inverting onto cooling racks to cool completely.

Whisk the sugar, lemon zest, and lemon juice in a medium saucepan. Whisk in the whole eggs and yolks in a small bowl and then whisk them into the lemon mixture.

Cook the mixture over medium-low heat, whisking constantly, until it's thick like pudding, about 6 to 8 minutes. Remove from the heat and whisk in the butter, a few pieces at a time until incorporated.

Strain the mixture through a fine-mesh sieve into a small bowl, pushing it through with a rubber spatula. Press plastic wrap directly onto the surface to prevent a skin from forming. Refrigerate until completely set, at least 4 hours and up to 5 days.

Heat the oven to 275 degrees F. Line a baking sheet with parchment paper. Set aside.

Crumble any clusters that are larger than 1/2 inch in diameter, and put the crumbs back in the medium bowl. Add the 1/2 cup milk powder and toss together until it is evenly distributed throughout the mixture.

Pour the white chocolate over the crumbs and toss until your clusters are covered. The crumbs will keep in an airtight container in the fridge or freezer for up to 1 month.

In the bowl of a stand mixer fitted with the paddle attachment, beat the butter until light and fluffy, about 2 minutes.

Turn the mixer to low and gradually add the powdered sugar, followed by the cream, salt and lemon extract. Mix until combined. Add yellow food coloring, if using. Mix until incorporated completely. Turn the mixer to medium-high and beat the frosting for about 5 minutes.

Use wooden spoon to beat the frosting by hand for about 2 minutes to push out any air pockets.

Spread a small dollop of frosting onto a cake board. Place the first cake layer, top side up, on the board.

Spread a thin layer of frosting over the cake layer and pipe a rim of frosting around the edge of the cake to create a barrier to the filling.

Spread about 1/4 cup of the curd in the center of the cake, carefully spreading it to the edge of the piping.

Sprinkle about a half cup to three-quarters cup of the lemon pretzel filling over the lemon curd. Gently pat into place.

Place a second cake layer on top of the piped frosting and filling and repeat these steps.

Place the final cake layer, top side up, on the second layer of filling.

Lightly coat the cake with a thin layer of frosting to lock in the crumbs. Freeze the cake for about 10 to 15 minutes to set the frosting.

Finish frosting and decorating the cake with the remaining frosting. Top with more lemon curd and lemon pretzel crunch filling.