In a large saucepan over medium heat, cook bacon until mostly browned. Add onion and cook with the bacon for 5 minutes. Remove the pan from the heat and stir in garlic for about a minute. Transfer the bacon and onion mixture to a heat safe bowl. Do not wipe out the pan.
Add the trimmed green beans to the pan. Pour in enough chicken broth to barely cover the beans, then bring to a boil over medium-high heat.
Add in red pepper flakes.
Cover, reduce heat and simmer for one hour. Check for tenderness, and continue to simmer if needed, up to 30 minutes more until beans are soft but not mushy.
Drain the chicken broth and return beans to the saucepan. Add bacon and butter and stir to melt and coat completely. Serve hot.
Notes
Using Frozen Green Beans - You can swap frozen green beans for fresh ones. The recipe will remain the same - simmer them in the broth for 45 minutes to an hour until very tender.Using Canned Green Beans - Instead of fresh or frozen, you can also use canned green beans. Make sure to drain and rinse them before adding and simmer until very tender.Storage - Leftovers can be stored in the fridge for up to 4 days.Reheating - For best results, reheat in a pan on the stove over medium. If needed, you can add a splash of water, broth, or a little more butter to remoisten them.