To a food processor, add the butter, flours, sugar, and salt. Pulse 10-12 times until the mixture resembles fine grains of sand.
Add in the egg/lemon mixture, vanilla extract, and 1 tbsp of the cold water. Process until the dough comes together and pulls away from the sides. If it remains a little dry, add a second tbsp of cold water, and so forth.
Knead the dough a few times on a floured surface and shape into a disk. Wrap tightly with plastic wrap and freeze for at least 30 minutes, or until ready to roll out.
Grease your tart tin or tins.
When rolling out, allow the dough 10 minutes to come to room temperature if taking from the freezer after an extended time. On a floured surface, roll out the dough to ¼ inch thick or so, cut out the area you need if making smaller tarts, and fold the dough over your rolling pin.
Gently lay the dough over the greased tart tin and unfold. Gently tuck the dough into the sides and bottom of the tin. Roll the rolling pin over the top of the tin and trim the edges. While turning the tin around, gently tuck the dough again into the bottom sides and start pressing up the dough slightly above each side groove as you create a little lip of dough over the top. It doesn't have to be huge, just a little extra to make up for blind baking shrinkage!
Wrap the tart/s in plastic wrap and freeze until ready. If blind baking right away, preheat oven to 350 degrees.
Gingerly add a double layer of aluminum foil to the tart tin/s, making sure to cover the top edges of the tart dough. Add pie weights or baking beans into the center of the foil and blind bake for 30 minutes if a full sized tart, or 10 minutes if mini tarts.
After the baking time has elapsed, remove the foil and weights/beans and continue to bake for 5-10 minutes if a full sized tart, and 5 minutes if a mini tart.
If saving the blind baked tart shells, leave in the tins and refrigerate.