Serves 16 Recipe

Prepare and Preheat

Preheat the oven to 350°F (175°C). Grease and flour four 9-inch round cake pans or two 9x13 pans (adjust bake times if using 9x13). Line the bottoms with parchment if available.

Whisk together dry ingredients: in a large bowl, sift or whisk 6 cups all-purpose flour, 4 cups granulated sugar, 4 tsp baking powder, 2 tsp baking soda, and 2 tsp salt until evenly combined.

Cream butter, oil and sugar: in the bowl of a stand mixer fitted with the paddle attachment (or using a hand mixer), beat 2 cups softened unsalted butter and 1 cup vegetable oil on medium speed until well combined. Add the 4 cups granulated sugar gradually and beat until light and fluffy, about 3–4 minutes.

Add eggs and vanilla: add the 10 large eggs one at a time, mixing 20–30 seconds after each addition until incorporated. Scrape the bowl as needed. Add 4 tbsp vanilla extract and mix until combined.

Combine dry and wet: with the mixer on low, add one-third of the dry flour mixture, then half of the 4 cups milk, mixing just until incorporated. Repeat with another third of the dry, remaining milk, then finish with the last of the dry ingredients. Mix only until there are no streaks of flour—do not overmix.

Divide and bake: divide the batter evenly among prepared pans (use a kitchen scale or measure to ensure even layers). Smooth the tops. Bake rounds for 25–30 minutes (or 9x13 pans for 30–40 minutes), or until a toothpick inserted into the center comes out clean and the top springs back when lightly pressed.

Cool: let cakes cool in the pans on a wire rack for 10–15 minutes. Run a knife around the edges, then invert onto racks to cool completely before frosting. If using 9x13 pans, cool completely in pan before removing or chilling to make frosting easier.

Make syrup: combine 1.5 cups water and 0.75 cup granulated sugar in a small saucepan. Bring to a simmer over medium heat, stirring until sugar dissolves. Remove from heat, stir in 1 tsp vanilla, and cool slightly.

Brush on layers: using a pastry brush, lightly brush the cooled cake layers with the syrup to add moisture. Use about 2–3 tbsp syrup per 9-inch layer, more if desired.

Beat butter: in a large bowl or stand mixer with the paddle attachment, beat 3 cups softened unsalted butter on medium speed until smooth, about 2 minutes.

Add powdered sugar: with the mixer on low, add 6 cups of the 12 cups powdered sugar to start, then increase speed to medium and beat until combined. Add the remaining powdered sugar in two additions, alternating with splashes of the 1 cup heavy cream, to reach desired consistency.

Flavor and finish: add 2 tbsp vanilla extract and 1 tsp salt. Beat on medium-high for 3–4 minutes until the frosting is light, silky, and spreadable. If frosting is too stiff, add more cream 1 tbsp at a time. If too thin, add more powdered sugar.

Level layers: if layers domed during baking, level them with a long serrated knife or cake leveler so they stack evenly.

Stack and fill: place the first cake layer on a serving platter or cardboard cake round. Spread about 1 to 1 1/2 cups of buttercream evenly over the layer (adjust amount to maintain even, stable cake). If using simple syrup, brush each layer before frosting.

Repeat: stack the remaining layers, spreading 1 to 1 1/2 cups buttercream between each layer. Reserve about 3–4 cups of frosting for the crumb coat and final cover.

Crumb coat: apply a thin layer of frosting around the entire assembled cake to lock in crumbs. Chill the cake in the refrigerator for 20–30 minutes to set the crumb coat.

Final frost: apply the remaining frosting to achieve a smooth finish. Use an offset spatula or bench scraper for clean sides. Smooth the top and create any decorative swirls or piping as desired.

Decorate: finish with sprinkles, fruit, or chocolate shavings as desired. Keep cake refrigerated if using perishable fillings or left in warm conditions; bring to room temperature 30–60 minutes before serving.