Fragrant Onion Tart

Ingredients

• 1½ pounds onions, preferably white (about 3 medium)
• 2 slices bacon (optional), cut crosswise into small pieces
• 2 tablespoons butter
• 1 heaping teaspoon fresh thyme leaves (or 2 pinches dried)
• sea salt
• freshly ground pepper
• 3 eggs
• ½ cup crème fraîche or cream
• ½ cup milk
• 1 cup grated aged Gouda or Gruyère cheese
• 1 cup plus 2 tablespoons white whole-wheat or spelt flour
• ¼ teaspoon salt
• 6 tablespoons butter (cut into small bits)
• 3 tablespoons ice water (or more if needed)