In a large mixing bowl, cream the butter and powdered sugar with an electric mixer on medium-high speed until smooth, 1-2 minutes.
Beat in the egg, vanilla extract, seeds scraped from the vanilla bean, and lemon zest until blended.
Mix in the flour and salt on low speed just until incorporated.
Form the dough into two balls, and flatten them into disks.
Wrap each disk tightly with plastic wrap.
Refrigerate until chilled and firm, at least 1-2 hours.
PREP OVEN AND PREP BAKING SHEETS:
When you are ready to bake the cookies, move the oven racks to the upper-middle and lower-middle positions and preheat the oven to 375 degrees F.
Line baking sheets with parchment paper or a silicone baking mat.
CUT OUT DOUGH:
Remove one dough disk from the refrigerator and roll it out on a well-floured work surface to ¼-inch thickness.
Cut with cookie cutters as desired and transfer to the prepared baking sheets.
BAKE AND COOL COOKIES:
Bake for 8-10 minutes, rotating the sheets halfway through baking until fully cooked but not at all browned.
Allow to cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.
Re-roll and cut the remaining dough. Repeat with the second disk of dough.
MAKE GLAZE AND ROYAL ICING:
In a medium bowl, stir together powdered sugar and meringue powder.
Stir in 5 teaspoons lemon juice and enough of the 4 to 5 tablespoons water to make a thin icing.
Transfer ½ cup of the icing into a small bowl and set it aside.
DECORATE COOKIES:
Using a pastry brush, paint cookies to the edges with the glaze.
Place the cookies on a wire rack to dry completely for about 30 minutes.
Beat the reserved icing with an electric mixer on high speed for 5 to 7 minutes or until peaks form.
Place the icing in a small resealable food-storage plastic bag; cut a very small hole in the bottom of the bag with the plain white icing.
Squeeze icing onto glazed cookies. Before icing dries, sprinkle with decorations, and tap off excess. Dry thoroughly on a cooling rack.
Dry thoroughly on a cooling rack. Serve.
Notes
This recipe makes about 30 cookies. How many cookies you get depends on the size of the cookie cutters. Cookie recipe adapted from Annie's Eats. Royal Icing adapted from Betty Crocker.If your dough becomes too soft and hard to work with, don't hesitate to pop it back into the fridge to chill again!