Fit 1 pie crust round into a 9-inch pie plate. Lightly prick the bottom of the dough with a fork.In a large bowl, toss together the blueberries, 1/2 cup sugar, cornstarch (use 3 tbs for a looser sauce or 4 tbs for a thicker sauce), 2 teaspoons lavender, lemon juice, and vanilla. Pour the berries into the crust. Arrange the butter pieces evenly over the berries. Grab the second pie crust round and roll it out into a 12-inch circle. Place the crust over the berries. Alternately you can create a lattice design if desired. Using a fork, crimp the edges of the crust together to seal the pie up. In a bowl combine 2 tablespoons sugar with 1 teaspoon lavender pinch the lavender and sugar together with your fingers to break the buds up into the sugar. Brush the top crust with the beaten egg and sprinkle with lavender sugar. Using a sharp knife, slice four holes in the top of the crust for air pockets. Cover and chill pie until crust is firm, 1 hour in the fridge or 30 minutes in the freezer. Preheat the oven to 400°. Bake for 20 minutes, then reduce the oven to 350 and bake another 30 minutes until the pie is golden and the sauce is bubbling.