preheat oven to 375. begin mashed vegetables; place cut potatoes and celery root in large pot; add cold water till covered. bring to boil, salt generously. cover and simmer until potatoes are easily pierced with fork (10-12 minutes). drain well; return to pot off the heat to dry.

begin the stew; heat 1 tbsp oil in large skillet over medium-high heat. add onion, garlic, mushrooms, and thyme; cook, stirring occasionally, until mushrooms are golden and soft (about 8 minutes). remove and spread along bottom of a 2 quart casserole dish. heat 1 tbsp oil in the same skillet; add the beef or lamb, carrot, rosemary, and nutmeg; cook u til beef is tender(about 8 minutes). stir in tomatoe paste. layer over mushroom-onion mixture.

Finish the mashed veggies pass potatoes and celery root through a food mill into a bowl adding butter as you go stir in yogurt and milk for a puree season with salt and pepper

Swirl mashed potatoes and celery root over stew with back of a spoon; sprinkle on cheese bake until cooked through and cheese is golden brown 15 minutes serve warm