Clean the morels thoroughly by splitting each in half and soaking them in cold water for 20-30 minutes. Remove from water, pat dry with paper towels, and chop into 1 inch pieces.
In a large pan, melt 2 tablespoons of butter. Add chopped morel mushrooms, rosemary, celery leaves and a small dash of salt and pepper as desired. Cook morels for 8 minutes on medium/low then turn and cook another 3 minutes. Remove morels from pan and set aside.
In remaining butter, cook thinly sliced shallot for 5 minutes. Remove from pan and set aside.
Add flour to the butter (adding the extra tablespoon if necessary). Mix thoroughly and cook for 1 minute. Add stock and water and whisk together until smooth.
Add cooked morels and shallots back into the pan. The sauce will thicken as it comes to a boil. Add additional salt and pepper to taste.
Remove from heat and serve over meat, potatoes or rice.