Celery casserole

In honor of Angie's Tasty Tuesday recipes, here a new one.

I had way too much celery in the vegetable bin (somehow I bought two) so I made up this variation of the classic green bean casserole.

Ingredients
4 cups sliced celery
4 tablespoons butter
3 tablespoons flour
1 cup milk
1 small can sliced mushrooms
1/4 red pepper, finely chopped
1 can French's onions

Directions
1. Saute the celery in the butter for five minutes or so (longer if you don't want the celery to be crunchy after baking).
2. Remove the celery and add the flour all at once (or, if you're lazy like me, move the celery off to the side of the pan and add the flour). Stir to incorporate flour.
3. Gradually stir in the milk. Make sure the roux (flour-butter mixture) dissolves.
4. Add the mushrooms and bell pepper, then remove from heat.
5. Add 1/3 of the French's onions.
6. Pour into a medium sized baking dish. I used a 1 quart oval Corningware baking dish. An 9x9 dish would probably also work.
7. Sprinkle 1/3 of the French's onions on top (you could probably use half in step 6 and half here, but I wanted to save some to top tomorrow night's salad).
8. Bake for 20 minutes at 350 degrees.
If the top starts to brown too quickly, loosely cover with foil.