Swiss Cheese Potatoes

8 lg potatoes, peeled and cubed
1 1/2 tsp salt, divided
2 c chopped celery
3/4 c chopped onion
1 1/2 c shredded swiss cheese, divided
2/3 c 2% milk
3 tbsp butter
1/4 tsp pepper

Place potatoes and 1 tsp salt in dutch oven; add water to cover. Bring to boil cook for 10 mins uncovered. Add celery and onion; cook 10-15 mins or until vegetables are tender. Drain and transfer to large bowl. Mash potato mixture; gradually adding 3/4 c cheese, milk, butter, pepper and remaining salt. Transfer to a greased 8 in square baking pan; sprinkle with remaining cheese. Broil 3-4 in for the heat for 5-8 mins or until cheese is lightly browned.