Almost no other food says spring like strawberries, and these petite butter cakes celebrate them in two ways. First, a traditional butter cake is perfumed and flavored with the fresh fruit, and then an exceedingly rich Swiss buttercream transforms into a red-speckled elegantly pale pink confection with the addition of strawberry jam. Making them the perfect sweet ending to a brunch, both the cakes and the buttercream can be prepared ahead. Wrapped well in plastic wrap, the cakes will keep in the refrigerator for up to three days and in the freezer for at least one month. The buttercream, too, stores well refrigerated or in the freezer (see the recipe for details). For an extra special detail, decorate the cakes with sugar decorations or flowers.
Strawberry Butter Cakes
Makes 10 cakes little cakes or about 20 cupcakes
4 large egg whites
1 cup sugar
Pinch of salt
1 pound (4 sticks) unsalted butter, at room temperature
1 teaspoon vanilla extract
1 1/4 cups strawberry jam
1 1/2 cups sifted cake flour
1 1/2 teaspoons baking powder
1/4 teaspoon salt
1/2 cup (1 stick) unsalted butter at room temperature
1 cup sugar
2 large eggs
1/2 cup milk
1 1/2 teaspoons vanilla extract
6 ounces fresh strawberries, hulled and cut into about 1/4-inch pieces
To make the strawberry buttercream, set a medium saucepan filled with about 1 inch of water over high heat and bring to a boil. Reduce the heat to low and maintain at slow simmer. Whisk together the egg whites, sugar, and salt in the bowl of an electric mixer. Set the bowl in the saucepan over the simmering water (the bowl should not touch the water) and, using the whisk, gently stir the mixture until the sugar begins to dissolve and it is warm to the touch (about 1 or 2 minutes). Immediately place the bowl on the mixer fitted with the whisk attachment and beat at high speed until the meringue is fluffy and cool, 5 to 7 minutes or so. Reduce the mixing speed to medium low and gradually incorporate the butter, about 1 tablespoon at a time, whipping until the buttercream is smooth and glossy and stopping once or twice to scrape the sides of the bowl. Incorporate the vanilla and strawberry jam, reduce the mixing speed to low, and continue to beat for another 2 to 5 minutes to dissipate any air bubbles. Transfer the buttercream to airtight containers or cover the mixing bowl with plastic wrap and set aside until the cakes are ready.
Preheat the oven to 350°F. Butter and flour 10 six-ounce ramekins and arrange on a large rimmed baking sheet, or line about 20 standard muffin cups with paper liners.
To make the strawberry cakes, whisk together the flour, baking powder, and salt in a medium bowl. Beat the butter in the bowl of an electric mixer fitted with the paddle attachment on medium-high speed until smooth. Add the sugar and beat until light and fluffy. Drop in the eggs, one at a time, beating until each one is fully incorporated. Stir together the milk and the vanilla extract. Reduce the mixing speed to medium low. Alternately incorporate the flour mixture and milk, beginning and ending with the flour and stopping several times to scrape the sides of the bowl, until the batter is thick and smooth. Remove the bowl from the mixer and fold in the strawberries.
Divide the batter between the prepared ramekins and bake until the tops are golden brown and a wooden skewer inserted in the centers comes out clean, about 25 minutes. Cool the cakes on wire racks in the ramekins until only slightly warm, at least 15 minutes.
Carefully run a paring knife around the edges to loosen the cakes and turn out onto another baking sheet or serving plate, or transfer the cupcakes to a wire rack to cool. Briefly whip the buttercream again on the machine or whisk by hand and pipe or spread onto the cakes, as desired. (Store the remaining buttercream in an airtight container for up to 3 weeks or in the freezer for up to 2 months.)