Directions
1. In a large saucepan with steep sides heat oil and butter and add onions, garlic, salt, and pepper.
2.Cook over medium high heat for 20 minutes, and then reduce heat to low and continue to cook for 45 minutes. The onions will begin to caramelize as they release their water. They should be a rich, deep golden color before proceeding to the next step.
3. Add flour and make a roux.
4. Add wine, then stock to create a thickened sauce, and add cream to finish it.
5. Add most of three quarters of the cheese to the sauce; reserving some for the top.
6. Stir in cooked potatoes and pour the mixture into a casserole dish.
7. Sprinkle with remaining cheese and bake at 350 ºF for 30 minutes.
8. Allow to rest for 20 minutes before serving.