Zest and juice remaining lemon to yield 1 teaspoon zest and 2 tablespoons juice. Whisk together zest, juice, and 1 cup powdered sugar in a small bowl until smooth.

Combine flour, baking powder, and salt; add to butter mixture alternately with ¾ cup milk, beginning and ending with flour mixture. Beat at low speed just until blended after each addition. Stir in 1 ...