• 6 tablespoons unsalted butter, plus a bit more for buttering the baking dish
  • 1 large yellow onion, finely chopped
  • 3 stalks celery, chopped
  • 3 cloves garlic, minced
  • 1/3 cup all-purpose flour
  • 2 cups whole milk
  • 3/4 cups half-and-half
  • 1/4 cup grated Parmesan
  • 1 teaspoon dry mustard
  • Kosher salt and freshly ground black pepper
  • 1-1/2 cup frozen peas
  • 16 ounces, weight Cavatappi noodles (rotini or elbow would be a good substitute)
  • 1/3 cup sour cream
  • 4 ounces, grated Gruyere cheese
  • 2 tablespoons chopped fresh dill, plus a bit more for garnish
  • 2 tablespoons chopped fresh chives, plus a bit more for garnish
  • 2 cans (5 oz. size) Albacore Tuna, drained, broken into 1/2-inch chunks
  • 2 cups coarsely crushed sour cream and onion flavored potato chips, or as needed