Heat oven to 375°. Line two baking sheets with parchment paper (aluminum foil may be used, but parchment paper works better with these cookies). In a large bowl, using an electric mixer, cream together butter and sugars until fluffy, about 2 minutes. Add molasses and vanilla extract, mixing until incorporated. Add egg and mix until light and smooth, about 1 minute on medium speed. Sift flour, salt, and baking powder over mixture; then, using a rubber spatula, fold dry ingredients into mixture. Use electric mixer to blend just until flour is incorporated. Divide dough in half and flatten into two disks. Wrap one disk in waxed paper and refrigerate while you work with the other disk. (Dough may be made up to this point and refrigerated up to 2 days.) Place disk between two large sheets of waxed paper and roll to ¼-inch thickness. Use cookie cutters to cut dough into desired shapes, such as stars, snowflakes, diamonds, or circles. Transfer cookies to prepared baking sheets, about ½ inch apart. Using a smaller cookie cutter or a knife, cut shapes into centers of cookies, reserving these center bits to add into extra dough. (You may also roll dough into long, thin ropes to make shapes. Do this on the baking sheets so you don’t have to transfer the dough.) Remove any wrappers on candies and separate them by color into plastic bags. Using a mallet or the side of a rolling pin, crush candies. (Note: If you use a wooden rolling pin, the candies may dent the wood.) Use a spoon to sprinkle the crushed candy into the hollowed-out centers of the cookies, filling to the edges. You can mix colors for a mottled effect. If cookies will be hung as ornaments or decorations, poke a small hole in the top of each cookie before baking. (Once cookies have cooled, thread string or festive ribbons through holes.) Bake 9 to 10 minutes. The candy should be melted and bubbling and the cookies just barely beginning to brown and firm to the touch. Remove baking sheets from oven and place on wire racks to cool. Allow cookies to cool on pans at least 10 minutes; otherwise, the candy centers may separate from the dough. When cookies are completely cooled, remove and store in an airtight container.