Preheat the oven to 180°C/350°F.
Make the mashed potatoes: Boil the diced potatoes in salted water until knife-tender. Drain and mash with butter, cream, salt, and pepper. Set aside.
Prepare the meatloaf mixture: In a large bowl, soak the bread in milk and Worcestershire sauce. Add grated onion, then mix in the beef, parsley, ketchup, garlic, egg, salt, and pepper. Combine without overworking the mixture.
Form and bake: Grease a muffin tin and divide the meat mixture into 8 portions. Press each portion into the tin. Bake for 15 minutes.
Make the glaze: Mix ketchup, brown sugar, Worcestershire sauce, and Dijon mustard in a small bowl.
Glaze the meatloaf cupcakes: After 15 minutes of baking, carefully pour the glaze over each meatloaf cupcake and return to the oven at 200°C/400°F for another 8-10 minutes until the glaze caramelizes and the meat is cooked through.
Top with mash: After baking, pipe or spoon the mashed potatoes on top of the meatloaf cupcakes. Garnish with chives and serve.