For the crust

1. Preheat the oven o 325 degrees F. Line a 9×9-inch baking dish with the parchment paper so it overhangs slightly over the edges. Lightly spray it with the nonstick cooking spray and set aside.
2. Add the flour, confectioners’ sugar, granulated sugar, and salt to a large bowl and whisk to combine.
3. Add the butter and lemon zest to the mixture. Use a pastry blender (or two forks), to mix the butter into the dry mixture until crumbly.
4. Transfer the mixture to the baking dish. Spread it evenly across the bottom, and pat it down firmly with your hands.
5. Bake until lightly golden, 30-35 minutes. Remove from the oven and place on a wire rack to cool slightly.

For the filling

1. Add the limoncello and lavender to a small saucepan over medium-high heat. Bring the mixture just barely to a boil, then turn off the heat and add a lid. Allow it to sit for about 15 minutes.
2. Strain the lavender from the liquid and discard. Set aside the liquid.
3. Increase the oven’s temperature to 350 degrees F.
4. Add the sugar and baking powder to a bowl, and mix to combine. Add the eggs, lemon juice and zest, and the limoncello. Mix well.
5. Pour the mixture over the crust and bake for 30-35 minutes or until lightly golden and slightly firm.
6. Cook on a wire rack. If you’d like, you can place the pan in the refrigerator for a bit to cool completely.
7. Use the overhanging parchment paper to remove from the pan. Cut into squares and sprinkle the tops with confectioners’ sugar.