Heat a large skillet or crêpe pan over just below medium heat. Line a wire cooling rack with parchment paper.
Melt the butter and set aside to cool slightly.
In a large bowl, whisk together the sifted flour, cornstarch, sugar, cinnamon, and salt.
In a separate large bowl, whisk the milk and eggs together until smooth. Microwave for 30-second increments, whisking in between, until bottom of bowl no longer feels cool. Add the butter while whisking and continue to whisk until smooth. Whisk in the vanilla extract.
Transfer the dry ingredient mixture to a very large pot*. Add the wet ingredients and whisk until completely smooth, making sure to wipe down the bottom and corners of the pot with a spatula to ensure all the dry ingredients get incorporated.
Rub the hot pan with butter and wipe off the excess with a paper towel.
Scoop up a scant 1/3 cup of batter and, holding the pan above the stove, pour the batter in the center while tilting the pan around to spread batter out towards edges of pan. Cook just until bottom side of crêpe turns golden (usually about 30-60 seconds). Flip carefully with your fingers or a large, flat spatula and cook until second side is golden in spots, similar to a tortilla. Remove from heat and set on parchment-lined wire rack.
Continue process until all crêpes are cooked, stacking them on top of one another to cool, with parchment in between each layer. Adjust the heat as needed if the crêpes are cooking too slowly or quickly, and butter the pan again if the crêpes start to stick at all. Whisk the remaining batter occasionally as you work. Once all crêpes are cooked, allow to cool completely before making fillings and assembling.
Place the chopped chocolate in a large, heat-safe bowl.
Microwave the cream for 2-3 minutes, until just starting to boil. Pour over chopped chocolate to cover. Let sit for 5 minutes, and then stir until smooth.
Set aside to cool to about room temperature, stirring occasionally to keep smooth; do not chill.
Cookie Butter Whipped Cream
Place cookie butter in a large bowl.
In the well-chilled bowl** of a stand mixer, whip the cream until firm peaks are just beginning to form. Add about 1/4 of the cream to the cookie butter and fold in until partially-combined. Continue to fold in the remaining cream, about 1/4 at a time, until all is added and the color is just even; do not overwork. Be sure to wipe along the bottom and sides of the bowl as you fold to get all of the cookie butter evenly mixed in.
Place in the refrigerator for about 15 minutes to cool before assembling cake.
Place the first crêpe layer on a cake round, cake plate, or serving dish. Spread a thin layer of ganache on top, leaving a bit of empty space around the edges of the crêpe. Place another crêpe on top and repeat with the cookie butter whipped cream. Continue until all crêpes are used, stirring ganache occasionally as you work to keep smooth.
To garnish, spread a thin layer of chocolate ganache on the top of the cake and top with chocolate curls as desired.Chill cake in fridge for a few hours, until set, before slicing.
The cake is good cold and will hold together best that way, but if desired, you can let individual slices warm up at room temperature, or microwave for 10-15 seconds to warm up. (With the latter options you risk having your slice tilt over and fall apart a bit, but it’ll still taste good!)
*You’ll need to use something big and tall that can hold the dry and wet ingredients while leaving room for rapid whisking.
*You can freeze your mixing bowl for 10-15 minutes to chill.