Preheat your oven to 400 degrees and have an 8x8 baking dish ready.
Chop the bacon into small pieces then add it to a medium skillet over medium high heat and cook until crisp.
Transfer the bacon to paper towel.
To the bacon drippings, add the flour while whisking. Continue whisking for 1 minute to fully cook the flour.
Whisk in the milk, sour cream, and cooked bacon.
Keep whisking until the mixture thickens. Remove from the heat.
Add in the green beans to the mixture and stir to fully coat the beans. Sprinkle with salt & pepper, to taste.
Pour the green bean mixture into the 8x8 baking dish and top with the fried onions.
Bake for 25-30 minutes.