Preheat the oven to 350 degrees F (175 degrees C). Grease a muffin pan with cooking spray.

Stir together bread crumbs, olive oil, and salt in a small bowl until well combined; set aside.

Bring a large pot of lightly salted water to a boil. Cook pasta in boiling water until tender yet firm to the bite, about 8 minutes. Drain and return pasta to the pot.

Stir beaten egg and butter into cooked pasta until pasta is evenly coated. Stir in mozzarella cheese, 1 cup Cheddar cheese, and milk until well combined. Spoon mixture into the prepared muffin tin. Sprinkle with remaining 1/2 cup Cheddar cheese. Sprinkle bread crumb mixture over the tops.

Bake in the preheated oven until the topping is nicely browned, about 30 minutes. Allow mac and cheese cups to set for a few minutes before removing from the pan.