Add ground beef to a bowl and add 2 tablespoons water, baking soda, 1 teaspoon salt and a pinch of pepper. Combine and let sit until onions are cooked.
Add olive oil to a 10 inch oven proof skillet, Add the onion and mushrooms along with ½ teaspoon salt and a pinch of pepper. Cook until they are soft. Add the ground beef and cook until browned.
Add the tomato paste and garlic and cook an additional 2 minutes. Add the Marsala wine and cook until it has evaporated.
Add chopped carrots, beef broth, Worcestershire sauce, thyme, and bay leaf and bring to a boil. Reduce heat to medium low and cook until the carrots are tender, about 10 minutes.
Combine cornstarch and a tablespoon of water and pour into the mixture, Add flour and cook about 1 minute. Remove bay leaf and thyme sprigs.
Turn the oven to broil and place the oven rack at least 6 inches from the broiler.
Top with mashed potatoes and smooth with a spoon. Place under the broiler for about 5 minutes until the mixture is bubbly and the potatoes have turned a golden brown.
