Beat 1 egg and sugar with an electric mixer until thick and pale.

Sift in flour and baking powder and add butter.

Beat on low speed until mixture forms a dough.

Wrap the dough in plastic wrap and chill until firm, about 1 hour.

Preheat oven to 350F.

Lightly beat remaining egg.

Roll level teaspoons of dough into balls.

Arrange dough balls 1 inch apart on ungreased baking sheets.

Press thumb into center of each ball to flatten, leaving a depression.

Brush lightly with remaining egg.

Sprinkle crushed sugar in centers.

Bake in batches in middle of oven until golden, 12 to 18 minutes.

Transfer to racks to cool completely.