First, preheat your oven to 375°F (190°C) and lightly grease a 12-cup muffin tin. In a large bowl, combine the ground chicken, diced onion, minced garlic, breadcrumbs, egg, parsley, Parmesan cheese, salt, and pepper. Use your hands to mix everything together until just combined, being careful not to overwork the mixture.
Using a scoop or your hands, divide the chicken mixture into 12 equal portions. Roll each portion into a ball and place it into one of the greased muffin cups. If you like, sprinkle a little extra Parmesan cheese on top of each one for a golden, cheesy crust.
Place the muffin tin in the preheated oven and bake for 22-25 minutes. The meatloaves are done when they are cooked through and the tops are lightly golden. You can use a meat thermometer to ensure they have reached an internal temperature of 165°F (74°C).
While the meatloaves are baking, you can prepare the sauce. Heat the olive oil in a small saucepan over medium heat. Add the garlic and sauté for about a minute until fragrant, then whisk in the flour and cook for another minute.
Gradually pour in the heavy cream while whisking constantly to prevent any lumps from forming. Continue cooking and whisking until the sauce thickens, which should take about 3-4 minutes. Stir in the Parmesan cheese and salt until the cheese is fully melted, then remove from the heat and stir in the fresh parsley. Let the meatloaves rest for a few minutes before drizzling the warm sauce over them and serving.