Mashed Potato And Rutabaga Gratin

advertise

Ingredients

2 oz. (4 tbs.) unsalted butter, softened; more for the baking dish
5 medium yukon gold potatoes (1-3/4 lb.), peeled and cut into 1- to 1-1/2-inch chunks
1 large rutabaga (about 1-1/2 lb.), peeled and cut into 1-inch chunks
kosher salt
8 oz. cream cheese, cut into 4 chunks, softened
1/2 tsp. dry mustard
1/2 cup (2 oz.) finely grated pecorino cheese
whole milk, as needed
kosher salt
freshly ground black pepper