In a medium bowl or measuring cup, combine and stir the egg whites, whole egg and the vanilla. Set aside.

In a bowl of an electric mixer, fitted with a paddle attachment, combine the dry ingredients together on low speed for 30 seconds.

Add the butter one piece at a time, about every 10 seconds. Once all the butter is added, pour in the buttermilk and mix on low for about 1 minute, until the ingredients are incorporated.

Scrape down the sides of bowl and begin to add the egg mixture in 3 separate batches, mixing on medium-low until light and fluffy, about two minutes. Fold once or twice to ensure the batter at the bottom of the bowl is incorporated and mix for another 20 to 30 seconds.

Using a kitchen scale, divide batter evenly among your pans (about 16 ounces of batter in each of the 8-inch pans or 12 ounces in each of the 6-inch pans), spreading evenly with a small offset palette knife.

Let the cake layers cool on racks for 10 minutes before inverting onto greased wire racks. Gently turn the cakes back up so the tops are up and cool completely.

Once the cakes are cooled completely, level the tops if needed.

Wrap each cake layer with plastic wrap and chill in freezer for at least an hour before using. The cake layers can be stored for up to a few days wrapped once in plastic wrap and frozen. To store longer than a few days, wrap twice in plastic wrap, then in foil, and seal in a zip-lock bag.

Heat the oven to 300 degrees F.

Combine the flour, cornstarch, sugar, cocoa powder, and salt in the bowl of a stand mixer fitted with the paddle attachment and paddle on low speed until mixed.

Add the butter and paddle on low speed until the mixture starts to come together in small clusters.

Spread the clusters on a parchment lined sheet pan. Bake for 20 minutes, breaking them up occasionally. the crumbs should still be slightly moist to the touch at that point; they will dry and harden as they cool.

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

In a stand mixer fitted with the paddle attachment, beat the butter until creamy, about one minute.

Turn the mixer on low and gradually add the melted butterscotch chips. Scrape the sides of the bowl and mix again for another 20 to 30 seconds. 

With the mixer still on low and gradually add the powdered sugar, followed by the vanilla, salt and heavy cream. 

Turn the mixer to medium-high and beat the frosting for about 5 minutes. Texture should be light and fluffy.

Stir by hand with wooden spoon to push out air pockets.

Heat the cream and then pour over the butterscotch chips. Stir until all the chips are melted.

After leveling each cake layer (if needed), place the first cake layer (top side/crumbly side up) on a cake board that has a little frosting on it (which acts like glue to hold the cake in place).

Spread about 1 cup of the frosting over the cake layer.Make sure to get eye level with the cake to check that your frosting is spread evenly across each cake layer. 

Sprinkle a handful of cookie crumbs over the frosting, followed by a drizzle of the butterscotch ganache.

Place the second cake layer on top and repeat step 2 and 3. 

When you get the final cake layer, place it top side down on the second layer of frosting. Spread a thin coat of frosting around the entire cake to lock in the crumbs. Freeze the cake for 10 minutes to set the crumb coat.

Continue to frost and decorate the cake with the remaining frosting.