Preheat the oven to 375°F. Lightly coat a standard 12-cup muffin pan with nonstick cooking spray.
Combine the panko breadcrumbs and milk in a large bowl. Let the mixture stand for 5 minutes so the breadcrumbs can soften.
Add the ground beef, ground pork, egg, onion, bell pepper, garlic, ketchup, Worcestershire sauce, Dijon mustard, smoked paprika, thyme, salt, and black pepper.
Gently mix the ingredients until evenly combined. Avoid packing or overmixing the meat, which can make the muffins dense.
Divide the meat mixture evenly among the 12 muffin cups. Gently shape and smooth the tops without pressing the mixture firmly into the pan.
Bake for 15 minutes.
While the meatloaf muffins bake, combine the glaze ingredients in a small bowl.
Remove the muffin pan from the oven and carefully brush the glaze over each meatloaf muffin. Return the pan to the oven and bake for another 7–10 minutes, or until the centers reach 160°F.
Meanwhile, place the potatoes in a large saucepan and cover them with cold water. Bring to a boil, reduce the heat, and simmer for 12–15 minutes or until fork-tender.
Drain the potatoes thoroughly and return them to the warm saucepan. Add the butter, warm milk, salt, and black pepper. Mash until smooth and creamy.
Allow the meatloaf muffins to rest in the pan for 5 minutes. Carefully loosen the edges and transfer them to a serving platter.
Spoon the mashed potatoes over the muffins or pipe them on with a large star tip. Garnish with chopped parsley if desired.
Serve two meatloaf muffins per person with additional vegetables or salad on the side.