Wash the potatoes and cut into 1" cubes. Place the potatoes in a pot and cover with cold water, add 2 teaspoons of salt, and bring to a boil.
Boil the potatoes for 15-20 minutes, or until they are fork-tender and no longer stick to a fork when pierced.
Drain the water, then add the potatoes back to the pot. Add in the butter, sour cream, salt, and garlic powder. Mash potatoes with a hand masher until smooth. Set aside.
Preheat oven to 400 degrees F.
Heat a large skillet over medium heat, then add the olive oil. Once hot, add the minced onion and cook until translucent and slightly golden. Add the minced garlic, salt, pepper, and ground beef and continue to cook until the beef is just slightly pink.
Add the frozen mixed vegetables, then sprinkle over the 2 tablespoons of flour. Mix, then add the beef broth, tomato paste, and Worcestershire sauce. Bring the mixture to a boil and continue to cook for 2-3 minutes to thicken.
Spray a deep 9" x 9" baking dish with nonstick cooking spray, then add the beef mixture and spread evenly into the bottom. Add dollops of the reserved mashed potatoes on top of the beef mixture. Cover evenly with shredded cheddar cheese.
Bake in the preheated oven for 20 minutes, or until the sauce is bubbling and the cheese is melted and golden brown. Remove from the oven and serve warm. Enjoy!