Combine the almond flour, tapioca flour, salt and coconut oil in a food processor and pulse.
Add an egg and process until the dough comes together.
Wrap the dough in plastic wrap and refrigerate for an hour.
When the hour is almost up, grind the lavender petals in a coffee or spice grinder. In a medium bowl, mix all of the filling ingredients together and set aside.
Preheat the oven to 375F.
Roll the dough out between two sheets of parchment paper into a 9-inch circle. Spoon the filling into the middle, leaving 2 inches around the perimeter. Use the parchment paper under the galette to gently fold the edges over the filling. Press down lightly to smooth out any cracks.
Beat an egg and brush the edges of the galette with it. Sprinkle some cane sugar on top.
Lift the parchment paper with the galette on top and place it on a baking sheet. Bake for 30-35 minutes until the galette is golden-brown and the blueberries are cooked.
Let cool for 15 minutes before cutting.