Beef Sheppard's Pie (Original Post 8/26/07)

Ingredients:
2 TBS extra virgin olive oil
3 TBS unsalted butter
1 medium onion, diced
3 medium carrots, peeled and sliced
1 rib celery, sliced
1/2 pound cremini mushrooms, quartered
2 cloves garlic, minced
1 TBS kosher salt
3/4 tsp dried oregano
3 TBS tomato paste
1 pound ground beef
1/4 C. canned low sodium beef broth
1/2 tsp Worcestershire sauce
Freshly ground black pepper
4 C. mashed potatoes
1/4 C grated Parmesan, optional
Directions:
Preheat oven to 350
Heat the olive oil and two table spoons of the butter in a large skillet over medium heat. Add the onion,carrot, celery,mushrooms, garlic, half the salt, and oregano. Cook until vegetables are tender, about 10 minutes. Stir in the tomato paste and cook until mushrooms are soft and the tomato paste has turned brick red, about 8 minutes more. Stir in the beef, the broth, the remaining salt, the Worcestershire sauce, and some pepper, breaking up any large clumps of meat, cook until meat is no longer pink, about 3 minutes.
Transfer the meat and vegetables to a 2-quart oval casserole dish and spread the mashed potatoes over the top, leaving a 1/4 inch boarder around the edge. Make a decorative pattern on the top of the potatoes if desired. Sprinkle with cheese, if using, and dot with the remaining tablespoon of butter. Bake until potatoes brown and the juices bubble around the edge, about 40 minutes. Let cool for 10 minutes before serving.