To Make the Lavender Sugar:
Place the dried lavender in the bowl of a food processor and blend it for 10-15 seconds to chop it into small pieces.
Add 1 cup of granulated sugar to the processor and blend well, for 15-20 seconds, until the lavender is finely ground and mixed into the sugar.
Whisk the lavender sugar together with the remaining 2¼ cups sugar until the lavender is well dispersed.To Make the Crust:
Preheat the oven to 350 degrees Fahrenheit. Line a 9×13 pan with foil so that it extends up the sides, and spray the foil with nonstick cooking spray.
In a bowl, whisk together the melted butter, lavender sugar, vanilla, and salt. Once mixed, add the flour and stir with a spatula until it is combined and no streaks of flour remain. Scrape the dough into the pan and press it into an even layer. It might seem a little greasy - this is normal.
Bake the crust for 25-30 minutes at 350 F, until it’s golden brown on top. While the crust is baking, prepare the filling so it’s ready to go as soon as the crust is done.To Make the Filling:
In a large bowl, whisk together the eggs, lemon juice, lavender sugar, and lemon zest. Sift the flour on top of the egg mixture, and whisk it in as well.
When the filling is done baking, slide the rack part-way out of the oven. Pour the filling over the hot crust and slide it back into the oven. Reduce the temperature to 325 F and bake for 25-30 minutes. It’s done when the center barely jiggles when you tap the pan.
Once done, remove the pan from the oven and let it cool until it reaches room temperature. For the cleanest cuts, refrigerate the bars and cut them when completely cold. To cut, remove the bars from the pan using the foil as handles. Use a large sharp chef’s knife and wipe it off often between cuts. Sprinkle the top with powdered sugar before serving, and add a few lavender buds on top if desired. Store Lavender Lemon Bars in an airtight container in the refrigerator for up to a week.