Place the chopped beef bacon in a large skillet or Dutch oven over medium heat. Cook, stirring occasionally, until the beef is browned and crispy, about 8-10 minutes.
Remove the crispy beef with a slotted spoon and set aside on a paper towel-lined plate. Keep approximately 2 tablespoons of the rendered beef fat in the pan.
Add the diced onion to the hot beef fat. Sauté for 3-4 minutes until the onion is translucent and soft.
Stir in the fresh green beans and toss to coat them in the flavorful fat. Cook for 5-7 minutes, stirring occasionally, until the beans start to blister and become tender-crisp.
Add the minced garlic and black pepper. Sauté for another minute until fragrant, being careful not to burn the garlic.
Splash the beef broth into the pan to deglaze, scraping up any browned bits from the bottom.
Return the crispy beef bacon to the pan and toss everything together. Add the butter (if using) and stir until melted and glossy.
Season with salt to taste and serve immediately.