2 large russet potatoes (about 1 pound)
1/4 cup whole milk
4 Tbsp unsalted butter, cut into pieces
4 ounces Cheddar, grated (1 cup)
kosher salt and black pepper
Microwave the potatoes on high until tender, 10 to 12 minutes. Halve lengthwise and, preserving the skins, scoop the flesh in a bowl. Mash the flesh with the milk, butter, 1/2 tsp salt, and 1/4 tsp pepper; mix in half the Cheddar. Spoon into the potato skins, place on a baking sheet, and sprinkle with the remaining Cheddar.
Bake at 450 degrees for 20-25 minutes, until golden.