Instructions

1. In a medium bowl, whisk the flour, rosemary, and salt together; set aside. Add the butter and granulated sugar to the bowl of a stand mixer (or a large bowl) fitted with the paddle attachment. Beat the butter and sugar until light and fluffy, about 2 minutes. Beat in the whole egg and vanilla until just combined. Add the dry ingredients from the bowl to the wet ingredients and mix on low speed until combined.
2. Divide the dough in half and place each half on a 16 x 12-inch piece of parchment paper. Shape each piece of dough into a log about 1 ½ inches in diameter, using the paper to roll and shape the dough. Seal up the ends with tape or tie with a rubber band and freeze for at least 1 hour. If you want to freeze the dough longer, transfer the frozen logs to a large zip-top bag; dough will keep up to 2 months.
3. Preheat the oven to 375° F. Line 2 baking sheets with parchment paper. Pour the coarse sugar into a long baking dish.
4. Brush one dough log with some of the beaten egg white. Roll the log in the sugar to coat the outside fully with sugar. With a very sharp knife, slice into ¼-inch rounds and set the rounds on the baking sheets - 20 rounds should fit nicely on a large baking sheet. They won't spread too much so don't worry about putting this many on the sheet. Repeat with the second dough log. If too much of the sugar falls off while slicing, you can roll the edges of the slices in the sugar individually. I found this method worked better for me.
5. Bake for 14-18 minutes, until the bottoms are golden brown and the sugar just starts to caramelized where it hits the baking sheet. Transfer the baking sheets to wire racks to cool for 5 minutes then transfer the cookies to the racks to cool completely before serving. 

Storage: Stored in an airtight container, the cookies will keep for up to 1 week.