Preheat the oven to 375 degrees . In a large pot of boiling, salted water, cook 1/2 pound large shell pasta until al dente; drain. Meanwhile, on a rimmed baking sheet, toss 1 cup coarsely chopped baguette with 2 tablespoons melted butter and bake until toasted, 5 to 7 minutes. In a medium saucepan, bring 1 1/2 cups dry white wine to a simmer. In a bowl, toss together 8 ounces shredded emmentaler cheese, 8 ounces shredded gruyere cheese and 2 tablespoons cornstarch, then gradually stir into the wine until melted. Stir in the cooked pasta and cook until the sauce is hot and runny. Pour into a serving dish and top with the bread cubes.