The day before baking, place the flour, softened butter, and baking powder in a large bowl. Rub everything together with your hands until the mixture feels soft and crumbly.

Work the sugar into the mixture by hand, then add the eggs and vanilla. Mix until the dough comes together.

Shape the dough into a ball, wrap it in plastic wrap, and refrigerate it overnight.

Let the dough sit at room temperature for a few minutes to soften slightly. Preheat the oven to 350°F and line baking sheets with parchment paper.

Roll the dough into 1 1/2-inch balls, press your thumb into the center of each ball, brush with beaten egg white, and sprinkle with pearl sugar or sliced almonds.

Bake the cookies for about 16 minutes, or until they are lightly golden. Move them to a wire rack to cool completely.

Store the cookies in an airtight container at room temperature or freeze for longer storage.