Sift together flour, baking powder, and salt into a bowl.
In another bowl, cream butter and sugar with an electric mixer on medium speed for 2 to 3 minutes, or until light and fluffy. Beat in egg and vanilla. Mix in flour mixture until dough is smooth and firm.
Divide dough in half and shape into two ½-inch-thick disks. Cover them in plastic wrap and refrigerate for 2 hours. (At this point the dough can be covered in plastic wrap, sealed in a zip- top plastic bag, and frozen for up to 2 weeks.)
Preheat oven to 325 degrees. Line several baking sheets with parchment paper.
Place dough on a lightly floured surface and dust dough with more flour. Gently roll each disk to a thickness of 1/8 inch. Using a cookie cutter, cut out cookies and then place about 1 inch apart on prepared sheets.
Bake for 10 to 15 minutes, rotating sheets halfway through baking, until edges are golden brown. Transfer cookies to wire racks with a metal spatula and let cool.
Decorate cookies with icing, colored sugars, and sprinkles. Use clean hands or kitchen tweezers to place jimmies on cookies in a decorative pattern. For flowers, place 1 dragée at the center of each blossom.