Absolutely Delicious Green Bean Casserole from Scratch

Step 1
Preheat the oven to 350 degrees F (175 degrees C).

Step 2
Place green beans in a saucepan and fill with about 1/2 inch water; bring to a boil. Cover and steam until beans are tender but still bright green, about 5 minutes. Drain.

Step 3
Combine drained beans in a bowl with mushrooms; toss to combine.

Step 4
Melt butter in a large skillet over medium heat. Add onion and parsley; cook and stir until onion is tender, 5 to 7 minutes. Whisk in flour until blended, then mix in lemon zest, salt, and pepper. Gradually whisk in milk, stirring constantly, so that no lumps form.

Step 5
Add sour cream and stir until combined. Warm over medium heat until sauce begins to bubble. Dump in green beans and mushrooms, stirring to coat.

Step 6
Remove from the heat and toss briefly with 1/2 of the Cheddar cheese and 1/2 of the French-fried onions. Spoon into a 1 1/2-quart casserole dish; top with the remaining Cheddar and onions.

Step 7
Bake in the preheated oven until Cheddar is melted, about 15 minutes.