Bring a large pot of salted water to boil. Cook the green beans for 5 to 7 minutes, just enough to soften them. Drain the water, and pour the green beans into the prepared dish.

In a medium saucepan, melt the butter over low-medium heat. Add the onions, and cook until they’re soft and translucent (about 5 minutes). Then add the garlic and cook an additional 30 seconds. Next, whisk in the flour, and continue to cook for 2 to 3 minutes.

Pour in the chicken broth, and whisk until smooth. Then add the milk and heavy cream. Whisk until the mixture begins to thicken (about 5 to 7 minutes). Add salt and pepper to taste, and remove from heat.

Pour the sauce over the green beans, then top with French fried onions.

Bake for 15 to 20 minutes. Cover with foil for the last 5 to 7 minutes if necessary to prevent the onions from over browning.

Serve warm, and store leftovers in the refrigerator for up to 3 days.