Mashed Potatoes:
Fill a medium pot with water and salt well. Heat the pot over medium-high heat until the water comes to a rapid boil. Add the cut potatoes and boil for 7 to 8 minutes, or until the potatoes can be easily pierced with a fork.
While the potatoes are boiling, add the butter and milk to a small saucepan. Heat over medium heat, whisking occasionally until the butter is completely melted. Alternatively, microwave the butter and milk in a microwave-safe bowl in 30-second bursts, whisking well between each burst until fully melted.
Once the potatoes are fork-tender, carefully drain all the water from the pot. Return the pot to the stovetop on an unused burner.
Mash the potatoes to your desired consistency using a potato masher or fork. Gradually stir in the butter-milk mixture, ensuring that all the liquid is well incorporated. Season the mashed potatoes with garlic powder, salt, and freshly cracked black pepper. Stir well to combine, then taste and adjust the seasonings as needed. Set the potatoes aside until ready to serve.
Ground Beef and Gravy:
In a large skillet, cook the ground beef over medium heat until browned and fully cooked, breaking it up with a spoon as it cooks. Drain any excess fat.
Add the chopped onion to the skillet with the ground beef and cook for 3-4 minutes until the onion is softened.
Stir in the garlic powder, salt, and freshly cracked black pepper. Pour in 1 1/2 cups of the beef broth, reserving the remaining 1/2 cup.
In a small bowl, whisk together the cornstarch and the reserved 1/2 cup of beef broth until smooth. Gradually stir the cornstarch mixture into the skillet with the beef, stirring constantly to prevent lumps.
Continue cooking the gravy, stirring frequently, until it thickens to your desired consistency (about 3-5 minutes). Taste and adjust seasoning as needed.
Serve:
Spoon the mashed potatoes onto plates and ladle the ground beef and gravy over the top. Serve immediately and enjoy this hearty, comforting meal.