Add the chopped potatoes to a pot of boiling water and cook until for tender. Drain and place back in the hot pot. Pour in the milk, butter, salt and garlic powder and mash until potatoes are light and fluffy. Set aside.
For The Cottage Pie
Preheat oven to 400 degrees F. If using a separate dish for the oven, spray it lightly with non-stick spray and set aside. *A 9x9" casserole dish should work.
Heat at least a 10" oven-safe skillet over medium-high heat and brown ground beef, breaking apart with a wooden spoon, until no longer pink. (Do not drain fat)**
Sprinkle in the onion soup mix and flour and stir until the mix and flour are absorbed into the ground beef and fragrant. Gradually whisk in the beef broth, and simmer until thickened.
Add in the vegetables and cook until heated through.
If using a separate dish for the oven, now is the time to transfer the beef mixture to it. Otherwise, carefully top the ground beef mixture with the mashed potatoes and spread out into an even layer. Top with the cheese and bake for 15 to 18 minutes, until bubbly throughout.
Video
Notes
**If using anything other than a lean beef, you might have quite a bit of fat left over after browning the meat. Drain the majority of the beef off, leaving about 1 to 2 tbsp left in the pan. HOW TO REHEAT: If preparing ahead of time, leave covered with foil and bake at 375 degrees until heated through. Refrigerated should take about 45 minutes, frozen can take about 60 to 70 minutes. If desired, remove foil towards the end to brown the top.