Preheat oven to 350°; spray 13 x 9-inch baking dish with cooking spray. In large skillet, cook sausage over medium-high heat 7 minutes or until browned, breaking up sausage with side of spoon.
Spread potatoes and sausage in prepared dish. In large bowl, whisk eggs, half & half, sage, salt and pepper; pour over sausage and sprinkle with cheese. Bake casserole 1 hour or until internal temperature reaches 160°; let stand 5 minutes. Cut casserole into 12 pieces; sprinkle with parsley, if desired.