Preheat oven to 350°F. Grease a 9 x 13 baking or similar size dish. Set aside.
Fill a large pot (10 quart) 3/4 full of water. Add green beans and bring water to a boil. Reduce heat and simmer green beans for 10 minutes. Remove from heat and drain.
In a large skillet, heat butter or olive oil over medium-high heat until shimmering.
Add garlic to the pan and cook until fragrant, about 1 minute. Add broth and heat until simmering.
Reduce heat to medium and add heavy cream, Dijon and Stone Ground mustard, lemon juice, salt, pepper and cayenne to the pan.
Stir and bring mixture to a low boil. Keep stirring until sauce begins to thicken.
Pour sauce over drained green beans and stir to coat. Transfer to baking dish.
Sprinkle fried onions over green beans.
Bake in 350° oven, uncovered, for 30 minutes and edges of pan start to bubble.
Remove from oven and serve.
Store leftovers tightly covered in refrigerator for up to one week.