Preheat the oven to 475 degrees F.

In non-stick skillet, saute onions in a little butter untill browned. Remove. Saute mushrooms, garlic and 1/2 tsp salt in a little more butter. Remove.

Melt 2T butter in the skillet and whisk in flour. Whisk in chicken broth. Cook for 1 minute.. Decrease the heat to medium-low and add the half-and-half. Cook until the mixture thickens, stirring occasionally, approximately 6 to 8 minutes.

Remove from the heat and stir in 1/4 of the onions and all of the green beans. Top with the remaining onions. Place into the oven and bake until bubbly, approximately 15 minutes. Remove and serve immediately.