How to Make Green Bean Casserole “Fry” the Onions: Coat sliced onions in some flour, then beaten egg + milk, then breadcrumbs. Bake. Blanch the Green Beans: Rinse fresh green beans, trim them, halve them, blanch them. Make the Gravy Sauce: Melt some butter with chopped mushrooms on medium-high heat. Add a little salt and pepper, then some garlic for flavor.
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