My Daddy would only eat carrots if they were creamed. Didn't matter if canned carrots or fresh but fresh is better. Found this recipe and thought it sounded good. If you don't have dry mustard or paprika and want to make it, then go for it. As that is the only addition I saw for the white sauce that I didn't do when making creamed carrots. The Parmesan cheese & the fried onion rings was a new addition to the party. As well, putting it in the oven as I always did my creamed carrots on the stove & carefully heated it up. AS TO THE FLOUR, you can trust your own instincts as to whether to use it.
Melt the Butter & then I would add the flour and cook it about a minute & make a sauce with the Mustard, Salt, Pepper, Paprika, & Milk. Thicken the sauce. (the recipe didn't have flour listed but every white sauce I have made is generally equal amount of butter to flour).
Peel the carrots & slice cross-wise on the bias. Cook covered in Salted Water until just tender, about 20 minutes. Drain & set aside. (don't cut into cute little circles, cross-wise I think cooks faster, from recall of reading tips).
Combine the Carrots & the Sauce, pour into a greased 1 1/2 quart casserole. Bake at 350 degrees for 30 minutes. Uncover & sprinkle on the Parmesan Cheese & French Fried Onions. Bake an additional 3 to 5 minutes.
The Parmesan cheese though listed as an ingredient the recipe failed to say where to use it. It could go into the sauce but I thought I would guess that it goes on top like you would do a nice pizza topping. Surely either way can't be all that bad?