In a medium mixing bowl, whisk together flour, baking powder, and salt. Set aside.
In the bowl of a stand-up mixer, cream together butter and sugar until light and fluffy. Add egg, vanilla, and lemon zest and mix until combined.
With the mixer on low, gradually add the flour, just until incorporated (do not overmix). Flatten dough into a disk and wrap in plastic. Refrigerate for at least 1 hour or overnight.
Preheat oven to 350 degrees. Line baking sheets with parchment paper or silicone baking mats.
Roll dough on a lightly floured surface to 1/2 inch thick and Use cookie cutters to cut into desired shapes. Place on baking sheet 1 inch apart.
Bake in preheated oven 12-14 minutes. Cool on baking sheets for about 7 minutes. Remove and finish cooling on a baking rack.
When cookies are completely cooled, whisk together the confectioners' sugar, lemon zest and 1 tablespoon of milk, at a time, until glaze reaches drizzling consistency.
Place cookies on a wire rack set over a sheet of foil and drizzle with glaze. Sprinkle with jimmies or colored sugar as desired. Allow cookies to sit on the rack until the glaze is fully set, about 3 hours.