Mise en place. Preheat the oven to 350 degrees Fahrenheit. Line two baking sheets with parchment paper. Measure and prepare all ingredients.
Prepare the dry ingredients. In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.
Infuse the sugar. In the bowl of a stand mixer, combine the sugar, dried lavender, and lemon zest. Rub everything together between your fingers for about 1 minute.
Cream the butter and sugar mixture. Add the butter to the stand mixer bowl. Using the paddle attachment, beat the butter and sugar on medium speed until light and fluffy, about 2-3 minutes. I always stop after a couple minutes and scrape down the sides of the bowl with a spatula and continue mixing.
Add the wet ingredients. Add the egg, lemon juice, and vanilla. Beat until combined. Scrape down the sides and bottom of the bowl as needed.
Add the dry ingredients. Add the flour mixture and beat on low until just combined.
Portion and shape the cookies. Using a medium-sized cookie scoop (I used #40 ~2 Tablespoons), scoop balls of dough onto the prepared baking sheets. Place the cookies 2-3 inches apart. I like to put 8 on each sheet, staggering the cookies. Roll each scoop of dough between your hands to form a ball then place the ball back on the baking sheet.
Bake. Bake one pan at a time for 11-13 minutes or until the edges are just set but the centers are still gooey. Be careful not to overbake! This will keep your cookies super soft. 12 minutes is perfect for my oven.
Cool. Remove the pan from the oven. Immediately "scoot" the cookies, reshaping them into perfect circles. Check out the recipe notes and video for tips on how to do this! Let the cookies cool on the baking sheet for 5 minutes. Transfer the cookies to a wire cooling rack and cool completely.