Roasted Potatoes and Onions with Vinegar and Thyme

Roasted Potatoes and Onions with Vinegar and Thyme
2 onion
6 medium red skinned potato
1 tbsp unsalted butter
4 tsp balsamic vinegar
2 sprig thyme
Preheat the oven to 350. Put the onions and potatoes in a baking dish just large enough to hold them. Melt the butter and pour it and the vinegar over the potatoes and onions. Season with salt and pepper and mix until coated. Bury the thyme sprigs in the vegetables and cover the dish with foil. Place in the oven to bake.  Stir occasionally during cooking and keep covered. Bake for 20-30 minutes or until potatoes and onions are light brown in color.