Tex-Mex Sausage Potato Casserole

3 Tbsps vegetable oil
1 Tbsp butter
1 med yellow onion – diced
1 celery stalk -chopped
1 lb Polish sausage – cooked and sliced
(2) 14.5 oz can Tex-Mex diced tomatoes
1/2 tsp salt
1/2 tsp pepper
8 med potatoes – peeled, cooked and cut up
1/4 cup shredded mozzarella cheese

• Preheat oven to 350 degrees. 
• Cook Polish sausage and slice into 1 inch pieces; set aside. 
• Peel and cut each potato into six, equal-sized chunks and boil until fork-tender; set aside.
• In a large sauté pan over medium-high heat add oil and melt in butter. 
• Add onion, celery and Polish sausage; sauté until onions are translucent. 
• Stir in diced tomatoes, salt and pepper; reduce heat and simmer for 10 minutes.
• Add potatoes and mix until thoroughly coated. 
• Transfer mixture to a 11” x 15” casserole dish, sprinkle with mozzarella cheese 
• Bake uncovered at 350 degrees for 40 minutes.