Preheat oven to 425 degrees. Heat a large skillet over medium-low heat and add butter. When butter is melted, add shallots and sea salt and saute. Cook until lightly golden, about 5 minutes. While shallots cook, thinly slice the potatoes. When shallots are cooked, add stock and thyme to the pan and scrape up any browned bits of shallot. Add potatoes to the pan and toss to coat.
Place half of the potatoes in the Good Cook Ceramic Oval Baker and top with ¼ cup of each cheese. Add the second layer potatoes and half of each of the cheeses into the Good Cook Oval Ceramic Baker. Top with breadcrumbs and remaining cheese. Cover lightly with foil and bake for 25 minutes. Remove the foil and bake for 10 more minutes to crisp bread crumbs and cheese.