Instructions

1. Using a hand mixer, beat the butter on medium speed for 1 minute until light and fluffy. Add both sugars and the salt and continue to beat on medium speed for 2 minutes until pale and creamy. Add the egg and vanilla seeds and mix on low to incorporate.
2. Add the flour and beat on low speed until the flour is nearly incorporated, then switch to a rubber spatula to incorporate the rest. Do not overmix.
3. Divide the dough into 2 portions. Place each portion in the center of an 18-inch-long piece of plastic wrap. Using a spatula, mold the mixture into a log about 7 inches long and 1 1/2 inches wide. Roll up the logs in the plastic and twist the ends together. Refrigerate the logs for at least 3 hours or until firm.
4. Preheat the oven to 350°F. Line a baking sheet with parchment paper. Remove the plastic wrap from one dough log and slice in ¼-inch rounds. Place the cookies 1 inch apart on the baking sheet. If desired, brush with the egg wash and sprinkle with sugar.
5. Bake for 15 to 20 minutes, or until the cookies are just beginning to brown around the edges. Cool for 5 minutes on the baking sheet before removing to a wire rack to cool completely. Repeat with the remaining dough.