Step 1: In a large bowl, cream together the softened unsalted butter and granulated sugar using an electric mixer until light and fluffy, about 2-3 minutes. Scrape down the sides of the bowl as needed.
Step 2: Beat in the large egg, lemon zest, and finely ground culinary lavender until just combined. If using, add the optional lemon juice at this stage.
Step 3: In a separate medium bowl, whisk together the all-purpose flour, baking powder, and salt.
Step 4: Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined. Be careful not to overmix the dough.
Step 5: Cover the cookie dough with plastic wrap and refrigerate for at least 30 minutes, or up to 2 hours. This chilling step is crucial for the best cookie texture and to prevent excessive spreading.
Step 6: Preheat your oven to 375°F (190°C). Line two baking sheets with parchment paper or silicone baking mats.
Step 7: Scoop rounded tablespoons of dough (or use a small cookie scoop) onto the prepared baking sheets, spacing them about 2 inches apart.
Step 8: Bake for 8-10 minutes, or until the edges are lightly golden and the centers are just set. The cookies may still look slightly soft in the middle.
Step 9: Let the cookies cool on the baking sheets for 5 minutes before carefully transferring them to a wire rack to cool completely.
Step 10: Once cooled, dust with powdered sugar or a mixture of granulated sugar and finely ground lavender for an elegant finish, if desired. Store in an airtight container at room temperature for up to 3-4 days.