9 Tb. (128g) cold unsalted butter, cut into small pieces
1 large egg yolk
Put all dry ingredients in a food processor and pulse to combine. Add the pieces of unsalted butter over the top of the dry ingredients, and pulse until the butter is cut in and the mixture looks like coarse meal. Break up the yolk a bit before you add it to the food processor, and then add it and process in long pulses until the dough comes together, you will hear the noise of the motor change.
Buttter a 9” fluted tart pan with a removable bottom, or six small pans. Press the dough evenly over the bottom and up the sides of the pan(s). You want to keep it crumbly here, it doesn't have to be perfect. Freeze crust for 30 minutes.
Preheat the oven to 375 degrees F. Place a piece of aluminum foil and fit it over the crust. Put the tart pan(s) on a baking sheet, bake the crust for 25 minutes (15 min for small pans), then remove the foil. Continue baking until the crust turns golden brown (don't let it burn!) about 8 - 11 more minutes (8 min for small pans).