Makes 4 4-inch cakes or 1 9-inch cake
Adapted from The Craft of Baking
8 ounces (2 sticks) unsalted butter, cubed, plus more for the pan
To make 1 cup of pistachio flour, grind 1 cup unsalted pistachios with 1 tablespoon flour in a food processor until fine.
In a large bowl, sift together the confectioners’ sugar, pistachio flour, cake flour, and salt. Add in the egg whites and whisk to combine. Slowing adding in the strained brown butter, whisking constantly. Cover the bowl with plastic wrap and chill in the fridge until it thickens up – at least an hour.
Preheat the oven to 350 F. Butter 4 4-inch springform pans. Note: To
make one large cake, use a 9 inch tart pan with removable bottom.
Place the pans on a large baking sheet and bake until the edges of the cake are golden and the top is slightly springy to the touch, 23-25 minutes (if you’re using 1 9 inch tart pan it will take 35-40 minutes). Transfer the cakes to a wire rack, removing the outer rings of the pans, and let cool.
The babycakes are best eaten warm or at room temperature the day they’re made, but can keep covered at room temperature for up to 3 days.