Mix the salt, pepper and paprika together and toss with the stewing beef in a bowl.
Heat 2 Tbsps of the oil in a large skillet over medium high heat. Brown the stewing beef til browned on all sides. Remove beef to a bowl.
Add remaining tablespoon of oil and heat it up. Add the onions and cook til soft about 7 minutes. Add the garlic and cook 1 minute more. Return the stewing beef to the pan.
Add the remaining goulash ingredients and mix well. Bring to a simmer, cover and allow to simmer over low heat on stovetop for approximately 2 hours.
Potatoes
While the stewing beef is simmering, peel and cube potatoes. Cover with water in a sauce pan. Bring to a boil over medium high heat. Allow potatoes to cook over medium/low heat until tender - about 20-25 minutes.
When tender, drain the potatoes and mash immediately. Add the butter and cream and beat until well mixed.
Allow potatoes to cool.
Mushrooms
Heat 2 Tbsps butter in a large skillet. Cook mushrooms over medium/high heat until they release their liquid and liquid evaporates. This can take 15-20 minutes.
Assembly
Spray a casserole about 10 X 3" with cooking spray. Layer the goulash on the bottom, spread mushrooms evenly over the goulash. Top with mashed potato mixture.
If serving immediately, preheat oven to 350 degrees. Bake casserole about 25 minutes until top begins to brown.
If freezing, allow casserole to cool. Cover tightly and freeze. When ready to serve preheat oven to 350 degrees, cook casserole from frozen until heated through, approximately 60 minutes.
Notes
Variation: After cooking onions and garlic and browning the stewing beef you can cook this in your slow cooker about 4 hours on high or 7-8 hours on low.