Makaroni Gratin

Bahan-bahan (4 porsi)

• 5 oz shrimp ((roughly 12 pieces))
• 8 oz boneless, skinless chicken thighs ((1–2 pieces))
• 2 Tbsp sake ((divided))
• 1 Tbsp extra virgin olive oil
• ⅛ tsp Diamond Crystal kosher salt ((divided; to season the shrimp and chicken))
• ⅛ tsp freshly ground black pepper ((divided; to season the shrimp and chicken))
• ¼ cup unsalted butter
• ½ onion ((6 oz, 170 g))
• 4 oz cremini mushrooms ((roughly 6 pieces; or use button mushrooms))
• 1 Tbsp mirin
• 6 Tbsp all-purpose flour (plain flour)
• 2½ cups whole milk
• ½ cup heavy (whipping) cream
• 1 tsp Diamond Crystal kosher salt ((to taste))
• ½ tsp white pepper powder ((to taste))
• 8 oz uncooked elbow macaroni ((roughly 2 cups))
• 1 Tbsp Diamond Crystal kosher salt ((for the pasta water))
• 2 oz Gruyère cheese
• 2 oz Parmigiano-Reggiano or Parmesan cheese
• 3 Tbsp panko (Japanese breadcrumbs)
• chives ((finely chopped, to garnish))