This really is The BEST Homemade Green Bean Casserole. Say by to cream of mushroom soup and hello to a homemade creamy mushroom sauce. Homemade french fried onions top this easy homemade casserole!
Preheat oven to 350 degrees. Grease a square baking dish (8x8 or 9x9 is fine).
For the casserole: In a large skillet, melt butter over a medium heat. Add onions, garlic and mushrooms. Sauté until softened, about 3-4 minutes. Add ½ teaspoon salt. Stir. Reduce heat to low and whisk in flour. Cook one minute. Slowly whisk in sherry. Cook 30 seconds.
Slowly whisk in whole milk and half half making sure to get all lumps out. Bring to a boil and then reduce to a simmer. Simmer until thickened, about five minutes. Add in remaining salt and Worcestershire sauce. Remove from heat.
Stir in green beans, mix until combined. Stir in 1/2 cup of fried onions. Transfer to baking dish and top with remaining fried onions. Bake until onions are golden brown and filling is hot and bubbly.
In a medium skillet, heat about ½ inch of canola oil. Heat to 375 degrees.In a small bowl, whisk flour, salt and black pepper. Place milk in another small bowl. Working in batches coat the onions first in the milk, then flour (shaking off excess) and then into the hot oil to fry. When the onions become golden brown, remove with a slotted spoon and drain on a paper towel.