This bistro classic is as refined as it is rich. We kept the filling onion-forward by cooking the strands in rendered bacon fat and stirring them into a light custard. Use yellow or white onions here; sweet onions will make the tart too sweet. Use a 9-inch tinned-steel tart pan. FRENCH ONION AND BACON TART Start to finish: 2 hours, 15 minutes Crust: 1¼ cups (6¼ ounces) all-purpose flour 1 Tbsp. sugar ½ tsp. salt 8 Tbsp. unsalted butter, cut into ½ inch cubes and chilled 2-3 Tbsp. ice water Filling: 4 slices bacon, cut into ¼ inch pieces Vegetable oil 1½ pounds onions, halved through root end and cut crosswise into ¼ ...