01 - Preheat the oven to 350°F. Line two baking sheets with parchment paper to prevent sticking and ensure even baking.
02 - In a medium bowl, whisk together the all-purpose flour, baking powder, and salt until thoroughly blended. Set aside for later use.
03 - In a large bowl, beat the unsalted butter and granulated sugar together using an electric mixer or hand whisk until the mixture becomes light and fluffy, approximately 2-3 minutes.
04 - Mix in the egg yolk, finely grated lemon zest, fresh lemon juice, and pure vanilla extract into the butter mixture until fully combined and uniform.
05 - Gradually add the dry flour mixture to the wet ingredients, mixing gently just until incorporated. Avoid overmixing to maintain tender texture.
06 - Fold in the finely chopped dried culinary lavender until evenly distributed throughout the dough.
07 - Scoop rounded tablespoons of dough and roll them into smooth balls. Arrange the dough balls 2 inches apart on the prepared baking sheets to allow for spreading.
08 - Gently press your thumb or the back of a teaspoon into the center of each dough ball to create a well for the lemon curd filling.
09 - Bake the cookies for 10 minutes. Remove from the oven and gently reinforce the thumbprint indentations if they have puffed up during baking.
10 - Fill each indentation with approximately 1/2 teaspoon of prepared lemon curd, being careful not to overfill.
11 - Return the cookies to the oven and bake for an additional 2 minutes, or until the edges become very lightly golden.
12 - Allow the cookies to rest on the baking sheet for 5 minutes before transferring them to a wire cooling rack to cool completely.