Preheat oven to 427F
Pulse panko in food processor about 5 times, till fine.
Grease a muffin tin with the butter. Coat the sides and bottom of each muffin hole with the ground panko crumbs.
Cut potatoes into 1/4" cubes. Place potatoes, half and half, salt, and pepper into a microwaveable bowl. Cover and microwave until potatoes are just starting to become tender, about 13 minutes, stirring once.
Combine the cheeses and corn starch. Set about a half cup of cheese aside for topping and mix remaining cheese with the hot potatoes. Stir until cheese is melted and smooth.
Distribute the potato mixture between the muffin cups. Sprinkle the reserved cheese over the potatoes. Cover with tin foil sprayed with oil. Bake for 10 minutes, remove foil, and return to oven for 13 - 15 minutes or until golden brown.
Loosen the sides of the potatoes and allow to sit for 5 minutes. Turn muffin tin upside down to remove the potatoes. Let cool another 5 minutes.