Blanch the green beans by bringing a large pot of water to a boil over high heat. When the water comes to a boil, add the green beans and cook for two minutes. Drain and rinse with cold water and then drain again. Set green beans aside.
In a large heavy pot (I use this one) with a well fitting lid turn the heat to medium-high, add butter and olive oil or just coat the bottom of the pan with olive oil, add sliced onions and sauté until that are just turning soft.
The onions will be melting at the end of the total cook time, and this adds a pleasant sweetness to the dish.
Add minced garlic to the would and let it cook for one more minute, stirring once.
Turn heat to low.Add green beans, chopped tomato, dill, and thyme.
(I use a diffuser on my gas burner element.)
Let cook on low for 40 to 50 minutes. The tomatoes should break down, and the beans will be tender.
Give the beans and gently stir and add salt and pepper to taste.
Add sauteed mushrooms at the end for more crowd-pleasing flavor.