Preheat the oven to 300ºF (150ºC).

Combine the sugars, cake flour, baking powder, salt, and rainbow sprinkles in the bowl of a stand mixer fitted with the paddle attachment, and mix on low speed until well combined.
- You can gauge when your ingredients are mixed based on the distribution of sprinkles throughout the mixture.

Combine the oil and vanilla in a small container or bowl and mix them together. Then with your mixer on low speed, stream the oil and vanilla in as close to the middle of the bowl as possible.
- The wet ingredients will act as glue to help the dry ingredients form small clusters, so continue paddling until these clusters appear. The largest crumbs should be no larger than a half-inch in diameter.
- Check the bottom of the bowl for any lingering dry ingredients and fold them in with a spatula.

Pour the crumb out onto a quarter sheet pan lined with parchment. Use your fingertips to spread the crumb out evenly.

Bake for 20 minutes, then check to make sure they are browning very slightly. The crumbs should contract just a bit to form individual boulder shapes when they're done—if they haven't yet, leave them in the oven for another two or three minutes. If you have an oven thermometer, check to make sure that your oven is at the correct temperature.
- If you plan on baking your cake sponge immediately afterward, you can clean up your space and start preparing the sponge recipe as the crumb bakes.

Let the crumb cool completely before using in a recipe. Stored in an airtight container, the crumb will keep fresh for 1 week at room temperature or 1 month in the fridge or freezer.

Preheat the oven to 350°F (175°C).

Combine the butter, shortening, and sugars in the bowl of a stand mixer fitted with the paddle attachment and cream together on medium-high for 2-3 minutes, just until it all comes together. Scrape down the sides of the bowl.

Crack the eggs into a small container. Add the eggs to the mixture one at a time with your mixer on low speed, making sure each is fully incorporated before adding the next. After you add each egg, you can increase the speed to high for a few seconds to help the ingredients incorporate.

Mix on high for 2-3 minutes. Scrape down the sides of the bowl once more, looking for any streaks of ingredients that haven't been incorporated.
- When it's done, the mixture should be light tan, glossy, and homogenous. If it looks like the ingredients are still distinct and trying to separate, cream for another 2-3 minutes. It's okay to see some sugar granules in the mixture.

On low speed, stream in the grapeseed oil toward the center of the bowl and then switch to high speed and paddle for 3-6 minutes until the mixture is practically white, twice the size of the original fluffy butter-and-sugar mixture, and completely homogenous.

Turn down your mixer to low speed and stream in the buttermilk and vanilla just a little at a time until fully incorporated.

Combine the cake flour, baking powder, salt, and 25 g rainbow sprinkles in a medium container or bowl and mix with a spoon. Add the dry ingredients into your mixing bowl. On the lowest mixer speed, mix for 45 to 60 seconds, just until the dry ingredients are well distributed.
- Scrape down the sides and bottom of the bowl thoroughly to ensure the batter is fully mixed. If not, keep lightly working the batter with your spatula until any dry ingredients are fully incorporated.

Spray an eighth sheet pan with baking spray in an 'X', line it with parchment, and spray the top of the parchment and the sides of your pan.

Pour the batter into the prepared eighth sheet pan and, using a spatula, knife, or the back of a spoon, spread the cake batter in an even layer.

Sprinkle the remaining 15 g rainbow sprinkles evenly on top of the batter.

Bake the cake for 30 minutes, checking intermittently for uneven browning. The cake will rise and puff, doubling in size.
- At 15 minutes, take a look at the cake with your oven light to see if any areas are browning more than others. If so, very gently rotate the cake in the oven (intense movement can cause your cake to deflate). For the next 15 minutes, you can check on the cake with the oven door
closed every 5-10 minutes and rotate if you see uneven browning.
- If you notice the cake is getting too much color on top but isn't set in the center yet, you can reduce the oven temperature to 325°F until the cake is baked through.
- At 30 minutes, use your finger to gently poke around the outside and center of the cake. It should bounce back very slightly and not be jiggly at all. Leave the cake in the oven for an extra 3-5 minutes if it doesn’t pass these tests.

When baked through, remove the cake from the oven and allow to cool to room temperature. The cooled cake can be stored in the fridge wrapped in plastic wrap for up to 5 days.

Combine the butter, shortening, and cream cheese in the bowl of a stand mixer fitted with the paddle attachment and cream together on high for 2-3 minutes until the mixture is smooth and fluffy. Scrape down the sides of the bowl.

Add the glucose, corn syrup, and clear vanilla extract and paddle on low speed until fully incorporated. Crank the mixer up to high and beat for about a minute until the mixture is silky smooth, glossy, and white. Scrape down the sides of the bowl.
- Pro Tip: Spray a spoon and small container with cooking spray to help measure your glucose so it doesn't stick too much.

Combine the confectioners’ sugar, salt, baking powder, and citric acid in a container or bowl and add to the stand mixer bowl. Start on low, then crank the speed up to high and mix for 3 minutes or until you have a stark white, beautifully smooth and fluffy frosting. It should look just like it came out of a plastic tub at the grocery store!
- Use the frosting immediately, or store it in an airtight container in the fridge for up to 1 week.

In a large mixing bowl, gently mix the cake and frosting together until a batter forms. Do not over mix the two ingredients together.

Form the batter into small balls, about 18 grams each, to make 30 total. Flattening the balls of dough creates a more cookie like shape versus a cake ball if it was left round.

Freeze the portioned out batter for about 30 minutes. This will help prevent the batter from falling apart when dipped into the melted chocolate.

Melt the chocolate in the microwave. Add the grapeseed oil and stir until it has fully incorporated.

Dip the cakes into the white chocolate until completely covered, before quickly tossing to coat with the cake crumb. Be sure to move fast, as the chocolate will set very quickly.

Store the crumb cakes in the fridge or freezer and enjoy!