Delicate, airy sponge cakes enriched with nutty brown butter, almond flour, and bright lemon zest, each crowned with a juicy fresh berry—elegant, light, and perfect for tea.
Brown the butter: Slice the butter and melt in a light-colored skillet over medium heat, stirring constantly. After 5–7 minutes it will foam, then develop browned specks and a nutty aroma. Once light caramel-brown, immediately pour into a heatproof bowl, scraping in the browned bits.
Reserve 2 tablespoons of the brown butter for greasing the pan. Cool the remaining brown butter (about 1/2 cup) in the refrigerator for about 30 minutes, until room temperature and no longer warm (do not let it solidify).
Preheat the oven to 350°F (177°C). Using a pastry brush, grease a 24-count mini muffin pan with the reserved 2 tablespoons browned butter. This recipe yields 30–36 tea cakes; prepare a second pan or plan to bake in batches. If using mini muffin liners, brush the liners with the brown butter.
Whip the egg whites: With a hand mixer or a stand mixer fitted with the whisk, beat egg whites on high speed until soft peaks form, about 2–3 minutes.
Add the dry ingredients: To the whipped whites, add almond flour, all-purpose flour, granulated sugar, baking powder, salt, and lemon zest. Beat on low speed until combined; the mixture will be thick and a bit lumpy.
Add vanilla and cooled brown butter: Pour in vanilla extract and the cooled brown butter; beat on low until a cohesive batter forms.
Portion and add berries: Spoon about 2 teaspoons of batter into each greased mini muffin cup. Lightly press a fresh berry into the center of each portion of batter.
Bake until the edges are golden brown and the tops spring back lightly to the touch. Cool briefly in the pan, then remove to a wire rack. Dust with confectioners’ sugar before serving, if desired.