step 1: Batter
In a small pan, cook the butter until brown like hazelnuts. Set aside. In another small pan, heat the milk until steaming; allow to cool for 10 minutes. In a mixer on medium-low speed, beat together the eggs, flour, sugar and salt. Slowly add the hot milk and browned butter. Pour into a container with a spout, cover and refrigerate overnight.
step 2: Pastry cream
Bring the milk with the vanilla bean (and scrapings) to a boil, then set aside for 10 minutes; remove bean. Fill a large bowl with ice and set aside a small bowl that can hold the finished pastry cream and be placed in this ice bath.
step 3: In a medium heavy-bottomed pan, whisk together the egg yolks, sugar and cornstarch. Gradually whisk in the hot milk, then place pan over high heat and bring to a boil, whisking vigorously for 1 to 2 minutes. Press the pastry cream through a fine-meshed sieve into the small bowl. Set the bowl in the ice bath and stir until the temperature reaches 140 degrees on an instant-read thermometer. Stir in the butter. When completely cool, cover and refrigerate.
step 4: Assemble the cake the next day
Bring the batter to room temperature. Place a nonstick or seasoned 9-inch crepe pan over medium heat. Swab the surface with the oil, then add about 3 tablespoons batter and swirl to cover the surface. Cook until the bottom just begins to brown, about 1 minute, then carefully lift an edge and flip the crepe with your fingers. Cook on the other side for no longer than 5 seconds. Flip the crepe onto a baking sheet lined with parchment. Repeat until you have 20 perfect crepes.
step 5: Pass the pastry cream through a sieve once more. Whip the heavy cream with the tablespoon sugar and the Kirsch. It won't hold peaks. Fold it into the pastry cream.
step 6: Lay 1 crepe on a cake plate. Using an icing spatula, completely cover with a thin layer of pastry cream (about ¼ cup). Cover with a crepe and repeat to make a stack of 20, with the best-looking crepe on top. Chill for at least 2 hours. Set out for 30 minutes before serving. If you have a blowtorch for crème brûlée, sprinkle the top crepe with 2 tablespoons sugar and caramelize with the torch; otherwise, dust with confectioners' sugar. Slice like a cake