Lentil Shepherds Pie

Name: Lentil Shepherds Pie
Ingredients: 3 pounds yukon gold potatoes, quartered; 4 Tbsp unsalted butter; 6 oz Pecorino Romano, grated; 1/2 cup milk or cream; salt & pepper; 1.5 cup dry green (not French) lentils; 4 cups Pacific Foods Organic Beef Broth (divided); 1 Tbsp olive oil; 1 large yellow onion, chopped; 2 cloves garlic, minced; 3 large carrots, chopped; 2 cups crimini mushrooms, quartered; 1 Tbsp tomato paste; 1 tsp fresh rosemary, minced; 1 tsp fresh oregano, minced; 2 cups frozen peas; 1/4 cup flour; 2 tsp red wine vinegar