1 c. (2 sticks) unsalted butter, at room temperature
1/2 c. granulated sugar
1 large egg
1 tsp. pure vanilla extract
1/2 tsp. kosher salt
2 1/4 c. all-purpose flour, spooned and leveled
Red and green gel food coloring
Sprinkles and sparkling sugar, for decorating
Preheat oven to 400°F. Line two baking sheets with parchment paper. Beat butter and granulated sugar with an electric mixer on medium speed until creamy, about 1 minute. Beat in egg, vanilla, and salt. Reduce mixer speed to low, and gradually beat in flour, just until combined. Divide dough into thirds. Tint 1/3 of the dough with red food coloring and 1/3 of the dough with green food coloring. Cover dough with plastic wrap.
Press white dough in desired shape through a cookie press onto prepared baking sheets. Repeat with red and green doughs. Decorate cookies with sprinkles and sparkling sugar, as desired.
Bake, in batches, until dry and set, 6 to 9 minutes. Cool on baking sheets about 1 minute, then transfer to wire racks to cool completely.