Makes four 4-inch-square cakes, serves 16
Softened butter, for pan
2 ¼ cups/315 grams cake flour
1 tablespoon baking powder
¾ teaspoon kosher salt, such as Diamond Crystal
1 ¼ cups/290 grams cultured buttermilk
2 large egg whites
1 whole large egg
¼ teaspoon pure vanilla extract
1 ½ cups/300 grams granulated sugar
4 ounces/113 grams unsalted butter, softened
Seeds scraped from half a vanilla bean pod
13 ounces/370 grams strawberry preserves (I like Bonne Maman brand)
Vanilla buttercream, recipe follows
2 quarts fresh strawberries, hulled and sliced
2 teaspoons finely grated lemon zest
About 12 fresh mint leaves
For serving: 4 quart-sized berry baskets
1. Prep: Butter a half-sheet (12-x-16-inch) pan.
2. Mix: In a large bowl, sift together flour, baking powder, and salt. Whisk to combine. In a measuring cup with a spout, whisk together buttermilk, egg whites, whole egg, and the vanilla extract.
3. Beat: Using a stand mixer fitted with the paddle attachment and medium speed, beat butter fluffy, about 2 minutes. Cascade in sugar, still beating. Beat in vanilla seeds. Switch to low speed. Shake in about one-third of the dry ingredients; mix. Pour in about half the liquid ingredients; mix. Mix in remaining doses of dry and liquid ingredients. Increase speed to medium-high and beat batter for 2 minutes.
4. Bake: Scrape batter onto prepared pan. Spread evenly with an offset spatula. Bake at 325 degrees in a standard oven or 300 degrees in a convection oven (low fan) until cake turns barely golden, feels springy to the touch, and pulls away from the sides of the pan, about 20-22 minutes. If your oven is uneven (like mine) rotate the pan after about 6 minutes of baking time. Let cake cool in pan. Turn out.
5. Stack: Set aside 3 tablespoons of the strawberry preserves. Spread cake evenly with remaining preserves. Chill until set, about 30 minutes. Using an offset spatula, spread with buttercream. Slice cake into 12 4-inch squares. Stack up four sets of three squares, buttercream-side up. Line the berry baskets with parchment paper, set one cake stack into each.
6. Gild: Zap the reserved preserves for a few seconds. Strain over sliced berries. Scatter on zest. Toss. Heap berries onto cakes. Scatter on mint leaves. Enjoy.
Vanilla Buttercream
12 ounces/ 339 grams unsalted butter, softened
4 large egg whites
1 cup/200 grams granulated sugar
1/4 teaspoon Diamond Crystal kosher salt
1 tablespoon pure vanilla extract
1. Beat: Using a stand mixer and the paddle attachment, beat butter soft and fluffy. Set aside.
2. Heat: Settle egg whites, sugar, and salt in a clean mixer bowl. Set the bowl over a pan of simmering water. Whisk until sugar has dissolved and egg mixture reaches 165 degrees, about 5-6 minutes.
3. Whip: Use mitts to return bowl to the mixer. Using the whisk attachment, whip on high speed to a glossy meringue. Lower to medium speed and whip until no longer hot. Add the reserved butter, 2 tablespoons at a time, whipping until buttercream smiles thick and smooth. Whip in vanilla extract.