Make the crust. Place a rack in the center of the oven and preheat to 325°F. Lightly grease 8 3-inch mini tart pans with cooking spray (make sure it's gluten-free). Pulse the nuts in a food processor until they are finely ground.
In a medium bowl, stir the nuts, sugar and salt until combined. Add the 4 tablespoons melted butter and the egg white, and stir the mixture with a fork until evenly combined.
Press about 1-2 tablespoons of the crust mixture into the base and up the sides of each of the prepared tart pans. You may need to use a bit of plastic wrap because the crust can be quite sticky.
Blind-bake the crust before filling. Bake for 17 to 20 minutes, or until it is rich brown and smells toasty. Transfer to a wire rack and let cool completely before adding the blueberry to the pans.
Make the blueberry curd. Pulse the lavender and sugar in the bowl of a food processor fitted with a steel blade attachment. Sift out any large bits of lavender with a sieve and set the sugar aside.
Slice the butter into small pieces and set it in a medium bowl with a sieve over it.
In a small pot, add the blueberries, lemon zest, lemon juice, and sugar. Cook on medium-low heat for about 20 minutes, stirring as needed until most of the blueberries burst and have released their juices.
Strain the blueberry mixture into the bowl with the butter to remove the blueberry skins. Whisk the butter until it melts then add the eggs, one at a time, whisking well after each addition.
Pour the blueberry juice back into the original pot (no need to do unnecessary dishes, right?). Cook over medium-low heat, whisking constantly until thickened and the temperature reaches 170°F. About 10-15 minutes.
Pour back through the sieve into a clean bowl to make sure it's entirely smooth. Pour into clean jars and store, tightly sealed in the refrigerator. The curd will last for a few weeks in the refrigerator.
Once the curd has cooled to at least room temp, pour it into cooled tart shells. Refrigerate until the curd has set, about 1-3 hours. Decorate the tops of the mini tarts with additional fresh blueberries, edible flowers or mint leaves. Keep in the refrigerator until serving.