Pulse the All-Purpose Flour (2 1/2 cup), Salt (1 teaspoon), Granulated Sugar (2 teaspoon), and Butter (1 cup) together until the butter is pea-sized. Add the Buttermilk (1/3 cup), and continue to pulse.
Once the flour sticks to itself when you squeeze it in your hands, dump out dough onto a floured surface, and work it together into a ball. Flatten dough into a disk, and cover with plastic wrap. Place in the fridge to chill for 30 minutes.
Mix the Fresh Blueberries (1.5 pound) together with the juice from the Lemon (1), Granulated Sugar (3/4 cup), All-Purpose Flour (1/3 cup), Ground Lavender (1 1/2 teaspoon), and Salt (1 pinch).
Preheat the oven to 400 degrees F (200 degrees C).
Roll out the dough into a 12-inch circle, adding more flour to the surface when needed. Transfer the dough onto a baking sheet or pizza stone. Dump the blueberry mixture in the center of the circle leaving a 2-inch margin around the edges.
Fold the edges of the dough in toward the center. Beat the Egg (1) to make an egg wash and brush the crust with the egg wash. Sprinkle with Coarse Sugar (to taste).
Bake in the oven for 40 minutes.
Let cool for at least 1 hour before serving.