Place oven racks in upper and lower thirds of oven and preheat oven to 350°F.
Combine flour, baking powder, and salt in a meduim bowl. With electric mixer on med speed, beat butter until creamy, about 1 minute.
Add sugar and beat until well blended, about 4 minutes.
Reduce speed to low. Beat in egg and vanilla until blended.
Add flour mixture, beating until well blended.
Stir in crushed candies.
Form dough by tablespoonfulls into 1-inch balls.
Place balls on 2 large ungreased baking sheets 2 inches apart. Firmly press top of each cookie with tines of fork to form crisscross pattern.
bake until cookies are golden on bottom and firm in center, 14-15 minutes, rotating baking sheets halfway through baking time. Let cookies cool slightly on baking sheets, about 3 minutes. Transfer cookies to racks and let cool completely. If making ahead, trasfer to airtight containers with wax paper between layers. Cover and store room temperature up to 1 week or freeze up to 1 month.