Bring a large pan of water to a boil on the stove top. Add the green beans and cook for about 5 minutes or until beans turn bright green and are tender crisp, about 3-5 minutes.
Remove beans from water and run cold water over them to stop the cooking process. Set aside.
Add butter to a large skillet or frying pan and heat over medium high heat. Add onions and cook until they just begin to brown.
Add in brown sugar and cook, stirring often until golden brown.
Pour in balsamic vinegar and stir to combine and deglaze the pan.
Transfer onions to a bowl.
Melt remaining 2 Tbsp butter in pan and add in beans.
Cook and stir until they begin to get brown spots and reach desired tenderness. About 8 minutes or so
Salt and pepper to taste.
Add in caramelized onions and crumbled bacon.
Notes
Do you not cook with fresh green beans because you don't like snapping the ends off the beans? Use a knife. I just line them up on a cutting board and cut the ends off!
Don't skip the blanching step. The beans will cook much quickly and more easily when you add them to the butter.
If you like, add in a teaspoon or two of minced garlic for additional flavor.