8 Tablespoons (4 ounces) unsalted butter, melted and divided
3 pounds Yukon Gold potatoes, peeled
Kosher salt and freshly ground black pepper to taste
3 Tablespoons fresh thyme, chopped
2 cups (8 ounces) grated Gruyère cheese
1 cup (4 ounces) grated Parmesan cheese
1 large tomato (10 ounces) cored and thinly sliced into 1/4-inch thick rounds
1 cup half-and-half
1 cup chicken broth
1/2 cup fresh bread crumbs
1/2 cup panko crumbs