Onion & potato Tarte Tatin

Tarte tatin is a traditional French open-faced tarte that can be sweet or savory.

1 prepared pastry crust
1 medium potato, sliced very thinly
1 medium onion, sliced thinly
2 Tbsp balsamic vinegar
butter
pinch of sugar
pinch of rosemary
salt and pepper

Butter an 8-inch baking dish well. Layer the sliced onions in the dish. Cover with sliced potatoes. Sprinkle with seasonings. Cut crust to fit the dish, then lay over potatoes. Bake in preheated oven at 425 degrees for 30 minutes.

Heat balsamic vinegar and sugar and reduce to a syrup.

Remove tarte from oven and immediately invert onto a warmed plate. Drizzle with balsamic syrup and serve hot.