1. 1. Preheat your oven to 350°F. This temperature ensures that the cookies bake evenly and develop a golden-brown exterior.

2. 2. In a large bowl, use an electric mixer or a stand mixer to cream together the salted butter and white granulated sugar until the mixture is light and fluffy.

3. 3. Once the butter and sugar are well-combined, beat in the two large egg yolks and the pure vanilla extract until thoroughly incorporated.

4. 4. Using a microplane or fine grater, zest the medium-sized lemon and add the fragrant zest to the dough.

5. 5. In a separate bowl, whisk together the all-purpose flour, chopped fresh rosemary, and salt. Gradually add this dry mixture to the wet ingredients, mixing just until the dough comes together.

6. 6. Roll the dough into small, uniform balls and place them on a baking sheet lined with parchment paper. Gently flatten each ball with your fingers, then sprinkle the tops generously with the sparkling sugar.

7. 7. Place the prepared cookie dough in the preheated oven and bake for 10-12 minutes, or until the edges are lightly golden.

8. 8. Remove the Rosemary Butter Cookies from the oven and let them cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely.