Prep ingredients: finely chop 3 large garlic cloves. Peel potatoes and cut into 1-inch pieces. Bring a medium saucepan of salted water to a boil. Cover and keep warm on low heat.
Prep meatballs: In a medium bowl, combine panko, ⅓ of chopped garlic, 1 large egg, ½ teaspoon salt, and ¼ teaspoon pepper. Let sit 5 minutes for panko to absorb the egg. Add beef and knead or stir to combine. form mixture into 10 equal-sized meatballs.
Make sauce: In a small bowl, add 1½ cups water, beef broth concentrate, cherry preserves, 2 tablespoons of the vinegar, 1½ teaspoons of the cornstarch , 1½ teaspoons sugar and mix.
Make potatoes & peas: Return saucepan of water to a boil. Add potatoes and another ⅓ of the garlic and cook until tender, about 8 minutes. Add peas and cook for one more minute. Reserve 3 tablespoons cooking water, then drain and return potatoes, peas, and garlic to saucepan. Add butter and coarsely mash, adding reserved cooking water to loosen. Season with salt, cover to keep warm.
Brown meatballs: In a medium nonstick skillet, heat 1 tablespoon oil over medium-high Add meatballs and cook turning once or twice, until browned but not cooked through, 6–8 minutes. Remove from heat.
Finish & serve: Stir remaining chopped garlic into skillet and cook over medium-high heat, 1 minute. Add sauce and season lightly with salt and pepper. Simmer, turning the meatballs in the sauce until sauce is glossy and meatballs are cooked through, 6–7 minutes. Spoon meatballs and gravy over mashed potatoes (reheat if necessary) and serve.