Preheat oven to 350°F (180°C). Grease muffin tins. With flour and salt in food processor, drizzle oil and pulse until bread crumbs form, then add just enough cold water so dough holds together. Roll out between two sheets of parchment paper (with a little more flour). Peel off top layer, place it back on, flip and peel off other side. Use cookie cutter or top of glass to cut circles. Press into tins and prick with fork. Cover with foil and heavy beans, and bake 10min. Fry bacon bits, shallots, and leeks in a little butter until soft, about 15min. Place in crusts. Whisk eggs and milk, add cheddar, and pour into crusts. Bake another 10min.