1. Whisk the flour, baking powder and salt together into a medium bowl. Beat the butter and sugar together in the bowl of an electric mixer on medium-high speed until light and fluffy, about 8 minutes. Beat in the peanut butter and egg. Turn the mixer to low and slowly add the flour mixture to make a smooth dough. Scrape the dough onto a piece of plastic wrap, flatten into a disk, wrap and refrigerate until firm, about 2 hours.
2. Position an oven rack in the center of the oven and preheat to 325°F. Spray the pressed cookie sheet molds with nonstick spray. Press the dough evenly into the molds; the molds should be three-quarters full.
3. Bake until the edges are golden, about 9 minutes. Remove from the oven and let the cookies remain in the molds for 5 minutes before turning them out onto a cooling rack. Repeat with the remaining dough.
4. Decorate the cookies as desired with Chocolate Ganache, Royal Icing and sanding sugars.
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