Line a 9 x 13" glass baking dish with parchment paper allowing the paper to hang over the dish for easier cutting. Set dish aside.
To make the crust, mix butter, sugar, vanilla extract, and Sel Magique together in a medium bowl. Add flour and stir to combine ingredients and create a thick dough. Press firmly into the pan so it's evenly thick (about 1/2"). Bake for 20 minutes or until the edges are lightly browned. Remove from the oven. Use a fork to puncture holes all over the crust top, making sure NOT to go all the way to the pan or to break the crust - this is to make sure the filling and crust bond together. Set pan aside.
To make the filling, sift the sugar and flour together in a large bowl. Next, add the eggs and lemon juice and whisk together until combined.
Pour the filling over the warm crust and bake 22-26 minutes or until the center sets and no longer jiggles. Remove from oven and cool at room temp about 2 hours. Refrigerate for 1-2 additional hours.
Lift the parchment paper out of the pan and remove the entire tart. Dust with confectioners sugar to taste, and cut into squares, and serve.