In a small bowl, zest all citrus fruits. Remove about 2 teaspoons of zest, combine with 1/2 cup granulated sugar, and set aside.

In a mixing bowl, cream together butter and remaining sugar until fluffy. Add the egg and mix well. Gradually add the flour, baking powder, and baking soda. Mix in the citrus zests.

Preheat oven to 350°F. Line baking sheets with parchment paper. Roll cookie dough into 3/4-inch balls, then roll in the sugar-zest mixture. Place on baking sheets and flatten slightly.

Bake for 10-12 minutes until edges are golden. Cool on wire racks. Store in an airtight container.