Preheat oven to 350°F (175°C).

Drain the can of green beans.

In a saucepan, melt 2 tablespoons of butter over medium heat.

Whisk in the flour, pepper, Accent (if using), and a pinch of salt.

Remove the saucepan from the heat.

Stir in the sour cream and mustard until smooth.

Return the saucepan to low heat and heat gently, but do not boil.

Add the drained green beans, grated Swiss cheese, and cooked minced onion to the sauce.

Stir until well combined.

Grease a casserole dish.

Pour the green bean mixture into the greased casserole dish.

In a separate small bowl, combine bread crumbs and 1 tablespoon melted butter.

Sprinkle the bread crumb mixture evenly over the top of the casserole.

Bake in the preheated oven for about 20 minutes, or until golden brown and bubbly.