Preheat your oven to 350 degrees F.
In the bowl of your electric mixer, beat the butter, flour, powdered sugar and vanilla extract until combined. It will be crumbly. Press it into a 9x13 inch baking dish. Bake it for 20 minutes, until slightly set.
While the crust is baking, whisk together the sugar and dried lavender. You can even do this a few days ahead of time to really flavor the sugar!
In the bowl of your mixer, beat together the 4 eggs and lemon juice. Beat in the lavender sugar, flour, lemon zest, vanilla and lavender extracts. Beat in the salt until combined. Pour the filling over the crust.
Bake for 25 to 30 minutes, until the top is slightly cracked and set. The inside filling will still be somewhat soft and curd-like! Sprinkle the lemon bars with powdered sugar. Let cool completely before slicing.
I like to store these in the fridge because they are delicious cold! You can always keep them at room temperature and slice too - they will be softer! Still delish.
Note: if you don't want to use the dried flowers, you can up the lavender extract to 1/2 teaspoon. If you don't want to use the extract, you can increase the dried flowers by an extra 1/2 teaspoon and also let the lavender sugar sit for a day or two!