I've been using some version of this crust for about 15 years, and over the years I've tweaked and fiddled and adjusted the basic recipe until I have something that works very well. Be sure you read the instructions and notes, as I've learned many lessons over the years!
Mix ingredients together thoroughly. If you're making a multiple-recipe batch (which I highly recommend, as I don't think this recipe is worth making for just one batch) I'd advise using a stand mixer with the paddle.
Form the dough into a ball, wrap in plastic and refrigerate until firm.
Taking out about half of the dough from the fridge at a time, divide the dough into small balls, 1/2 ounce apiece (if you have a kitchen scale and want to use it) and press the dough into the wells of a 24-cup min-tart pan. It's not a bad idea, especially if you're going to be using a fruit-based filling, to use foil mini-muffin liners. Use of these liners will remove any possibility of sticking to the pan. Try to get a little rim of dough to stick up above the edge.
I’m afraid there’s no alternative to just using your thumbs—even Martha Stewart does it that way. (I do have a pastry tamper, and for the last few batches I used that first and then went back around with my thumbs, but I’m not sure I saved any time that way. I may try to refine my technique a bit the next time.)
If you're making the shells ahead of time, you can put the pans with the shells in the freezer, let them get hard, and then pop the shells out and put them on a baking sheet.