With hands, rub together butter and sugar.
When sugar is absorbed, mix them thoroughly for 2 minutes with the help of a whisk or a beater.
Add the egg and mix for 2 minutes.
Add flour and make a dough. The dough should not be sticky. Add more flour if it's sticky. (you can use chilled water 2tbs if having problem making the dough)(*** If you are using a stand mixer, add the cubed butter, sugar, salt and vanilla to a stand mixer fitted with a paddle attachment. Mix for about 2 minutes or until it's homogeneous) Add the egg yolks and mix until combined.
Add the flour and mix until shaggy, about 45 seconds.
Once the dough is made cover with the sheet of a plastic wrap and keep in the fridge for 30 minutes to make if firm.
Preheat the oven at 190c (gas mark) or 375 degrees F.
After 30 min take out the dough and dust the surface with flour.
Roll out the dough until a slightly thin sheet is formed then cut it with a cutter of any shape (I used a round cutter)
Now transfer these roundels to your tart molds, pressing into the corners and fluted sides of the pan.
Run the rolling pin over the top of the pan so that the excess dough gets cut off, make the edges clean.
Patch any edges that are too thin with excess dough, trimming away the edge again as necessary.
Prick the bottom with a fork and keep them in the freezer for 10 minutes again.
When ready to bake the tart shell,s keep them in the preheated oven and bake for 15 to 20 minutes or until the tart shells are fully baked and golden.
Cool completely before filling.
Note: You can store the tart shells in large airtight boxes and use as required.