Heat the oven to 375°F. Lightly grease 8 cups of a standard muffin pan.
In a large bowl, whisk the egg and milk. Stir in the dry stuffing mix and let it sit for 2 minutes so the crumbs begin to soften.
Add the ground beef, Italian seasoning, black pepper, and 1/4 cup of the Parmesan. Add 1/4 cup of the marinara. Mix gently until combined, taking care not to pack the meat mixture too tightly.
Divide the mixture among the 8 prepared muffin cups. Press it in lightly, leaving the tops slightly rounded.
Spoon the remaining 1/4 cup marinara over the muffins. Bake for 25 to 30 minutes, until the centers reach 160°F.
Sprinkle the remaining Parmesan over the tops. Let the muffins rest in the pan for 5 minutes before serving.