Ingredients

3/4 cup (105 g) all purpose gluten free flour blend (I used my basic gum-free blend)

1/4 teaspoon xanthan gum (omit if your blend already contains it)

2 tablespoons (18 g) cornstarch

3 tablespoons (18 g) finely ground nonfat dry milk (can replace 1:1 with extra flour blend but your brownies will be a bit denser)

1/4 teaspoon baking powder

1/4 teaspoon kosher salt

1/4 cup (50 g) granulated sugar

1 tablespoon finely grated lemon zest (from 1 lemon)

2 tablespoons freshly-squeezed lemon juice (from 1 large lemon)

3 egg whites (75 g) + 1 whole egg (50 grams, weighed out of shell) at room temperature, beaten

4 tablespoons (56 g) unsalted butter, at room temperature

1/3 cup (40 g) confectioners’ sugar

2 teaspoons finely grated lemon zest (from 1 small lemon)

1 to 2 teaspoons freshly-squeezed lemon juice