Preheat oven to 350°F (180°C). Spray 2 (8- inch) round cake pans with baking spray with flour.

In the bowl of a stand mixer fitted with the paddle attachment, beat butter, granulated sugar, Vanilla Sugar, and oil at medium speed until fluffy, 3 to 4 minutes, stopping to scrape sides of bowl. Add eggs, one at a time, beating well after each addition. Beat in Vanilla Extract.

In a medium bowl, whisk together flour, baking powder, and salt. With mixer on low speed, gradually add flour mixture to butter mixture alternately with milk, beginning and ending with flour mixture, beating just until combined after each addition. Divide batter between prepared pans (about 712 grams each), smoothing tops with a small offset spatula. Tap pans on a kitchen towel-lined counter several times to settle batter and release any air bubbles; smooth tops again, if necessary.

Bake until a wooden pick inserted in center comes out clean, 35 to 40 minutes. Let cool in pans for 10 minutes. Run a knife around pans to loosen edges of cake layers; remove from pans, and let cool completely on wire racks.

Level cooled cake layers, if desired. Place 1 cake layer on a serving plate or cake turntable. Generously brush Vanilla Simple Syrup onto cake layer. Using a small offset spatula, spread 1⁄4 cup (48 grams) Vanilla Bean Buttercream evenly onto cake layer. Spoon 1⁄2 cup (96 grams) buttercream into a pastry bag, and cut a 1⁄2-inch opening in tip; pipe a 1⁄2-inch border of buttercream around edge of cake layer. Using a small offset spatula, spread Vanilla Custard in an even layer within piped border. Top with remaining cake layer, cut side down, and brush with Vanilla Simple Syrup. Using a large offset spatula, spread a thin layer of buttercream on top and sides of cake to create a crumb coat. Refrigerate for 30 minutes.

Spread remaining Vanilla Bean Buttercream on top and sides of cake. Using a small offset spatula, texture sides and swirl top as desired. Garnish with Vanilla Sugar, if desired. Store in the refrigerator covered 3 to 5 days.