Heat the green beans according to package directions.
Meanwhile, in a 12" skillet, melt 4 tablespoons butter on medium. Whisk in flour and cook, whisking constantly, 2 minutes, until flour has darkened slightly in color and mixture is smooth. Slowly add milk, whisking constantly to smooth out any lumps. Heat until sauce comes to a simmer and thickens slightly.
Remove from heat and stir in Gruyere by handfuls until smooth. Season with salt and pepper to taste. Stir in green beans, then transfer to a 2-qt. baking dish.
In a 10" nonstick skillet, melt remaining 2 tablespoons butter on medium-low. Stir in bread crumbs and cook 2 to 3 minutes, until golden brown, stirring often. Season with salt and pepper to taste. Remove from heat and stir in chives. To serve, sprinkle crumbs over green beans.
Source: Hannaford fresh Magazine, October November 2023