Using the paddle attachment of the mixer, cream the butter and sugar over medium speed for 3-4 minutes
Add the egg, salt and vanilla and mix until combined. Use a spatula to clean down the sides and bottom of the mixer bowl
Finally add the flour little by little. Do not overmix
Divide the dough in two and flatten each one into a disk. Wrap each disk in plastic and refrigerate for at least 2 hours or overnight
Over a floured surface and using a rolling pin, roll each disk until 1/4" thick and cut into 3" circles. If needed add a bit more flour
Place each circle into a 2.5" diameter tartlet plan and using your fingers, press into the bottom and every groove. Tartlets pan don't need to be greased
Freeze for 20 minutes or until firm
Preheat oven 350 Degrees F
Prick the bottom of each tart pan with a fork
Bake for 12-15 minutes or until golden
Remove from mold by simply inverting them into a cooling rack and let them cool completely