Crust: Preheat the oven to 375º. Put the flour, sugar and salt in the bowl and pulse a few times to mix. Dump in all the butter and pulse about 15 times total. You want to cut the butter up smaller than you would for a flaky pie crust. Add in 2 tablespoons of the ice cold water and turn the machine on for 5-6 seconds. You’ll know that you have the right amount of moisture in the dough by removing the lid, reaching in and grabbing a handful, squeeze it together and if it clumps…it’s perfect. If it is still crumbly and does not stick together, then put the lid back on, add another ½ to 1 teaspoon of ice water and turn on again for another 5-6 seconds.
Press dough in tart pan. Try and make it an even layer across the bottom of the pan.
To avoid shrinkage place it on a plate and put it in the freezer to firm up and rest for at least 30 minutes.
Cook bacon until crispy. Less 2 tablespoons of drippings in pan and cook onions on low/med heat with thyme & salt, covered 20mins. So not brown, sweat the onions. Pull crust out of the freezer, place it on a cookie sheet, add a sheet of foil on top and press it in gently and then fill with your favorite pie weight (dry beans, rice, actual pie weights, marbles, ball bearings). Place in the oven for 30 minutes while the onions are cooking.
Beat the eggs and add in the half and half, a grind or two of black pepper and a touch of salt, mix well and set aside. The onions, they should be translucent, soft and very fragrant. Remove them from the heat and cool long enough that they won’t cook the eggs. When the crust comes out, remove the pie weights and foil. Remove the thyme sprigs from the onions and mix them into the custard. Pour it all into the tart crust, sprinkle with bacon pieces and put it back in the 375º oven for 25-30 minutes on the middle rack.