Winter Portabella Mushroom Stew - cooking recipe

Ingredients

4 tablespoons olive oil
1 large onion, cut into 1/2-inch dice
2 teaspoons chopped fresh rosemary
8 ounces portabella mushrooms, sliced 1/2-inch thick, gills removed
1 lb large white mushroom, thickly sliced
1 (14 1/2 ounce) can diced tomatoes
3 tablespoons tomato paste
2 garlic cloves, minced
1 teaspoon sherry wine vinegar
2 tablespoons butter (optional)
salt & fresh ground pepper, to taste
2 pinches red pepper flakes

Preparation

Heat 1 tablespoon oil in large nonstick skillet over medium heat.
Add onions and rosemary and cook stirring occasionally, until lightly browned, about 12 minutes; remove to a bowl.
Return the pan to the stove and add half the remaining oil.
When it's hot, add the portabella mushrooms and saute until nicely browned, about 5 minutes.
Add portabellas to the onion mixture and repeat sauteing with the remaining oil and the white mushrooms.
Return everything to the pan and add the tomatoes, tomato paste, garlic, 1-1/2 cups water and vinegar.
Simmer gently for 12 to 15 minutes, then swirl in the butter.
Season with salt, pepper and red pepper flakes.