Preheat your oven to 375°F and prepare a 2-quart baking dish by greasing it.

In a small saucepan, melt the butter over medium-low heat. Add the shallots and sauté until soft and translucent—about 4 minutes. Stir in the garlic and cook for another 30 seconds, then remove from heat.

Using a box grater or food processor, shred the cooled, baked potatoes while keeping the skin on.

In a large bowl, mix together the sour cream, salt, black pepper, 2 cups of the cheddar cheese, along with the sautéed shallots and garlic. Gently fold in the shredded potatoes until just combined, being careful to maintain the texture.

Transfer the potato mixture into the prepared dish. Top it off evenly with the remaining cheddar and the parmesan cheese. Bake everything for 25-30 minutes or until it achieves a lovely golden brown color.