French Onion Tart

Instructions

• WHIRL flour with salt in a food processor. Add butter and pulse until coarse crumbs form. Gradually add 1/4 cup ice water and vinegar, pulsing after each addition. Pulse just until dough starts to come together. Gather into a ball, then press into a disc. Wrap in plastic wrap. Refrigerate at least 45 min or up to 3 days.

• HEAT a large non-stick frying pan over medium. Add oil, then onions and shallots. Cook, without stirring, for 5 min. Reduce heat to medium-low. Add salt and sugar. Season with pepper. Cook, stirring often, until onions turn deep brown, 6 to 12 more min. Set aside.

• WHISK eggs with cream and milk in a medium bowl until smooth. Set aside.

• PREHEAT oven to 400F. Lay an 11-in. fluted tart pan on a baking sheet. Cut out a foot-long piece of parchment paper. Roll dough on a lightly floured surface into a 13-in. circle, about 1/4 in. thick. Carefully lift dough into tart pan. Gently press dough into the corners and up the edges of the pan. Trim and discard excess. Prick the dough with a fork about 15 times. Lay parchment on the shell and fill with 2 cups dry beans or pie weights.

• BAKE in centre of oven for 15 min, then cover with foil. Continue baking until shell is just golden, about 15 more min. Remove to a rack. Reduce heat to 350F. Lift out parchment and beans. Reserve beans for future use.

• SPRINKLE half of cheese, then onion mixture over warm crust. Add egg mixture. Sprinkle with remaining cheese, then thyme.

• BAKE in centre of oven until top is firm, 20 to 22 min. Transfer to a rack.Let tart rest 10 min before serving.