Place the beef cubes in a large slow cooker. Top with the garlic, carrots, mushrooms and corn. In a medium bowl, whisk together the beef broth, tomato paste, Worcestershire sauce, oregano and House Seasoning. Pour the mixture over the contents of the slow cooker and stir to combine. Cover and cook on low for 7 to 9 hours, or high for 3 1/2 to 4 1/2 hours, until the beef is tender.
To make the mashed potatoes, place the potatoes in a large saucepan and cover them with 2 inches (5 cm) of water. Bring the potatoes to a boil over high heat and stir in the salt. Reduce the heat and simmer until the potatoes are tender when stabbed with a fork (start checking them at 15 minutes).
Drain the potatoes, and return them to the pot. Add the milk, butter, salt and pepper to taste. Gently mash the potatoes with a handheld potato masher.
Use a large spoon to skim any fat from the surface of the beef and veggie mixture in the slow cooker. In a small bowl, mix the flour and 6 tablespoons (90 ml) water until smooth, then slowly stir the mixture into the slow cooker. Add the peas. Adjust the seasonings to taste with salt and pepper. Mix the cheddar into the Mashed Potatoes and spread in an even layer over the top of the beef and vegetables. Cover the slow cooker and cook on HIGH for 15 to 30 minutes, until the gravy is thickened and the Mashed Potatoes are heated through.
*Many of the recipes in this cookbook call for House Seasoning. This House Seasoning Recipe is as follows: 1/4 cup fine sea salt, 1/4 cup garlic powder, 2 tablespoons onion powder, 1 tablespoon black pepper. Mix these together in a small bowl and store the House Seasoning in an airtight container.