Bring a large pot of water to a rolling boil. Add fresh green beans and cook them for 1 minute. Transfer beans to an ice water bath to stop the cooking process.

In a large skillet over medium-high heat, melt 1 tablespoon of butter. Add sliced onions, seasoning with salt and pepper. Cook for 5-8 minutes until soft, then reduce heat and cook for about 15 minutes until caramelized.

Stir in minced garlic and sauté for another minute until fragrant. Set the onion mixture aside.

In the same skillet, heat another tablespoon of butter over medium heat. Add the blanched green beans with salt, pepper, and red pepper flakes. Sauté for 1-2 minutes until heated through.

Gently fold in the caramelized onion mixture with the green beans and warm together for an additional minute. Serve immediately.