First, form the crust. Get out a 9-inch removable bottom tart pan and spray it really well with Nonstick Cooking Spray (to taste). Combine the All-Purpose Flour (225 gram), Powdered Confectioners Sugar (25 gram), and cubed Butter (11 tablespoon) in the bowl of a food processor. Pulse them together until it becomes pebbly.
Add in the Egg (1) and Water (2 tablespoon) and continue to run the processor until it forms a ball. Turn it out onto a floured surface and roll it out to be slightly larger than the tart pan. Press the dough firmly into the tart pan to form the crust, leaving a little dough to hang over. Then chill it in the refrigerator for 30 minutes.
Preheat the oven to 350 degrees F (175 degrees C).
Get the tart shell out of the refrigerator when the 30 minutes is up. Line it with aluminum foil and fill it with dry beans or pie weights. Blind bake the crust for 12 minutes to crisp it up.
Remove the foil and beans and bake it for another 10-12 minutes to dry out the bottom. Take it out and let it cool.
Reduce the oven heat to 320 degrees F (160 degrees C). While the tart crust bakes and cools, make the filling.
Just whisk the Granulated Sugar (350 gram), zest and juice of the Lemon (6), Egg (9), Heavy Cream (1 1/2 cup), and Ground Lavender (1 teaspoon) together thoroughly until it is smooth and luscious.
Pour it into the cooled crust and place the whole tart on a sheet tray. It just makes it easier to take it in and out of the oven. Let it bake at the gentle temperature for 50 to 55 minutes. It should be set but still have some wobble to it.
Let it cool for half an hour, then gently remove it from the tart shell by hold the bottom and letting it slide off. Chill for at least 3-4 hours to overnight.