Step 1

In a medium bowl, whisk together flour, baking powder, and salt. In a large bowl, using an electric mixer, beat butter and sugar on medium-high until light and fluffy, 3 minutes. Add egg yolks and vanilla and beat to combine. With mixer on low, gradually add flour mixture and beat to combine. Form dough into 2 disks, wrap in plastic, and refrigerate 30 minutes.

Step 2

Preheat oven to 350 degrees, with racks in upper and lower thirds. Working with 1 disk at a time, roll out dough between floured parchment paper to 1/8-inch thickness. Stack dough in parchment on a baking sheet; refrigerate until firm, 30 minutes. With a 2 1/2-inch Christmas-ball-shaped cutter, cut out dough (reroll scraps, if desired). Place cookies, 1 inch apart, on two parchment-lined baking sheets. With a 1-inch star cutter, cut out dough in center of each cookie. Bake until cookies are pale but set, 8 to 10 minutes, rotating sheets halfway through. Remove sheets from oven; fill cutouts with crushed candy. Bake until cookies begin to brown at edges and candy is melted, 3 minutes. Let cool completely on sheets on wire racks.