Directions1. Heat butter in a 12-inch saute pan. Add onions, salt and sugar and toss well. Cook over high heat for 5 minutes, stirring frequently.
2. Reduce heat to medium and cook for about 30 minutes until onions are soft and golden brown.
3. Add the dark rum or water, pepper, thyme and parsley and cool for 10 minutes.
4. Fill the pastry shell with the cooked onion mixture.
5. Mix together the eggs and cream and pour into the pastry shell over the onions, leaving a bit of space so it doesn't overflow when it bakes.
6. Bake in a 350° oven for 30 minutes, preferably on an oven stone, until the tart is lightly browned. Unmold immediately (place tart on top of a large soup can and let the ring fall off). Let cool on a rack. Serve warm or at room temperature.
Note: You can used a purchased pie dough for the pastry shell -- either one already in the tin or dough that you roll out and place in your own tart or pie pan.