You can use Idaho, red, or gold potatoes for the mashed potatoes.
Peel potatoes and cut them into about 1 inch chunks. Cutting the potatoes will make it faster to cook and easier to mash. (If you want to leave skin on, make sure to wash potatoes well.)
Place potatoes into a cooking pot and pour in enough water to cover the potatoes. Add bay leaf and season water with some salt and pepper. Cook potatoes over medium heat until potatoes are tender enough to be pierced with a fork easily.
Drain potatoes but save some cooking water. Add butter, heavy cream, about 1/4 cup of cooking water, garlic powder and salt. Mash potatoes until all lumps are broken and it’s smooth. If you need to, add another 1/4 cup or so of cooking water to reach desired consistency. Mashed potatoes should be soft enough to easily spread over the beef.
Preheat a large (12-inch) cooking pan over medium heat. Saute diced onions and carrots until softened and add minced garlic. Saute until garlic is fragrant.
Add ground beef and break it up into as many pieces as possible. Season the beef with some salt and pepper, cover and let it cook until browned about half way. Stir and break up as many lumps as possible. Add peas and corn, cover and cook for a few more minutes, until meat is browned.
While meat is cooking, heat up beef broth and mix it with Worcestershire sauce and tomato paste. Set it aside.
Sprinkle flour over the beef and stir well until flour is evenly incorporated.
Pour in beef stock mixture and stir it in carefully. Add herbs and taste to see if more salt and pepper is needed. Stir and cook for a few minutes, until the gravy is thickened.
To Assemble Shepherd's Pie:
Preheat oven to 375° and lightly grease a 9×13 casserole dish.
Spread beef mixture evenly over the bottom of the casserole dish. Spoon mashed potatoes over the beef mixture and gently spread it over the top.
Bake it for 30-35 minutes, until golden brown on top.
TIP: Shepherd’s Pie can be made ahead of time. Prepare it up to the step of baking and instead of baking it, cover it air-tight with plastic wrap or aluminum foil. Put away into the refrigerator. When ready to bake, take of the cover and bake for 35-40 minutes.