- 1 cup (5 ounces) all purpose flour
- 1/4 teaspoon salt
- 1 stick (8 tablespoons) unsalted butter, at room temperature
- 1/4 cup (1 2/3 ounces) sugar
- 2 tablespoons confectioners sugar
- 1 tablespoon vanilla extract
- 1 egg yolk
- 2 teaspoons zest and 1 tablespoon juice from about 4 small key limes
In a small bowl, whisk together flour and salt; set aside. In a large bowl, cream together butter, sugar, and confectioners sugar until creamy, about 3 minutes. Beat in vanilla, egg yolk, juice, and zest until combined. Add flour and salt mixture and beat just until dough comes together. Form dough into two 1 1/2-inch wide logs and wrap in plastic wrap. Let chill in refrigerator at least one hour.
Adjust oven rack to middle and upper positions and preheat oven to 350°F. Line two baking sheets with parchment paper. Slice logs into 1/4-inch coins. Bake until coins are just golden on the bottom, about 20 minutes. Let cool for 5 minutes then transfer to a wire rack to finish cooling.