In a large bowl, sift together flour, salt, and baking powder; set aside. In the bowl of an electric mixer, cream the butter and sugar until fluffy. Beat in eggs. Add flour mixture, and mix on low speed until thoroughly combined. Stir in vanilla or lemon juice and zest. Wrap dough in plastic, and chill for about 30 minutes.
Preheat oven to 325 degrees F.
On a floured surface, roll dough to a 1/8-inch thickness. Cut into desired shapes. Transfer to ungreased baking sheets, and refrigerate until firm, 15 minutes. Remove from refrigerator, and transfer to oven to bake until edges just start to brown, 8 to 10 minutes. Cool on wire racks.
Cover with a thin coat of royal icing, and allow to dry for 24 hours. Using a pastry bag fitted with a coupler and #3 or #4 tips, pipe designs onto cookies. Use a #70 tip to create the "leaves."
2 large egg whites, or more to thin icing
4 cups sifted confectioners' sugar, or more to thicken icing
Juice of 1 lemon
3 drops glycerin (optional)
Paste or gel food coloring
Beat the egg whites until stiff by not dry. Add sugar, lemon juice, and glycerin; beat for 1 minute or more. If icing is too thick, add more egg whites; if it is too thin, add more sugar. Add food coloring sparingly until you achieve the desired shade.
Consumption of raw or undercooked eggs, shellfish and meat may increase the risk of foodborne illness.
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