String Beans In Azeri Tomato Sauce(Azerbaijan) - cooking recipe

Ingredients

1 lb of fresh string bean, trimmed
4 tablespoons butter
2 onions, sliced thinly into crescents
Azeri Tomato Sauce
8 ounces tomato sauce
2 tablespoons of finely chopped fresh basil
1 teaspoon salt
1/2 teaspoon ground black pepper
1/4 cup plain yogurt
1/4 cup sour cream
2 teaspoons white vinegar (or more to taste)

Preparation

Melt the butter in a saute pan set over medium heat. Add the onions and lower the heat, stirring occasionally for 3-5 minutes. Add the green beans, stir and cover to cook for 20-30 minutes - stirring occasionally - or until the beans begin to soften to your desired consistency.
If you haven't made the tomato sauce at an earlier time, it can be prepared as the beans cook.
When the beans are almost done but not quite, pour in a desired amount of tomato sauce and allow them to simmer on low for a few minutes. Remove from heat and serve.
Tomato Sauce:
In a small to medium saucepan, stir in the tomato sauce and half of the basil and all of the pepper. Cook 3-5 minutes or until warmed. Stir in yogurt, sour cream, and vinegar. Cover and cook another 5 minutes - stirring often. Stir in remaining basil and salt cook another 3-5 minutes and pour over the green beans, vegetables or meat.