Lightly brown pork in butter in skillet. Remove meat. Cook celery, onions and mushrooms in same skillet until tender, about 5 minutes.
Prepare Sauce: Dissolve bouillon cube in 3/4 c. boiling water and stir flour, salt and pepper, blending until smooth. Add to vegetables and cook until thickened, stirring constantly. Stir in sherry. Pour sauce over pork. Cover and bake 1 1/2 hours at 350 degrees.