• Gather all the ingredients. For the cooked rice, please note that 1½ cups (300 g, 2 rice cooker cups) of uncooked Japanese short-grain rice yield 4⅓ cups (660 g) of cooked white rice, enough for 4 servings. See how to cook short-grain rice with a rice cooker, pot over the stove, Instant Pot, or donabe.
  

To Prepare the Ingredients

• Grease the gratin dishes with ½ Tbsp unsalted butter.
  
• Using the tip of a sharp knife or hands, cut off the smaller stalks of 1 head broccoli from the larger central stalk to remove whole florets, rotating the head of broccoli as you go. Prepare a medium bowl of ice water.
  
• Bring a small saucepan of water to a rapid boil. Add ¼ tsp Diamond Crystal kosher salt. Add the broccoli florets and cook until crisp-tender, 1 to 1½ minutes. Remove with a fine-mesh sieve and plunge immediately into a bowl of ice water to stop the cooking. Drain and set aside.
  

To Make the Butter Rice

• Chop ½ onion finely and cut 4 mushrooms into thin slices.
  
• In a large frying pan, heat 1½ Tbsp unsalted butter over medium heat. Add the onion and sauté until tender.
  
• Add the mushrooms and sauté until tender. Then add 4 servings cooked Japanese short-grain rice. Break up the big chunks of rice and combine well.
  
• Season with ⅛ tsp Diamond Crystal kosher salt and ⅛ tsp freshly ground black pepper. Divide the rice into 4 portions and transfer the rice to the individual gratin dishes. Cover with aluminum foil and keep warm.
  

To Make the Seafood Mix

• Clean 16 manila clams and 24 baby scallops, and peel and devein 12 large and jumbo shrimp. (For tips, see my posts on how to clean clams and devein shrimp.) Cut the bodies of 4 small calamari into rings. Finally, cut 2 cloves garlic into thin slices.
  
• In a large frying pan, heat 2 Tbsp extra virgin olive oil and cook the sliced garlic on medium heat until fragrant. Then, add all the seafood to the pan.
  
• Stir fry to coat the seafood with oil. Add ½ cup white wine and cover with a lid. Cook until all the clams open up.
  
• Once all the clam shells are open (dispose of any unopened ones), season with freshly ground black pepper. Then, remove all the seafood to a plate/bowl and cover with aluminum foil. Set aside.
  
• Simmer the remaining seafood sauce in the frying pan until the sauce is reduced in half, roughly ¼ cup. Keep the sauce in a bowl or measuring cup.
  

To Make the Bechamel Sauce

• First, make a roux. In a large frying, heat 4 Tbsp unsalted butter on medium-low heat. Once melted, add 4 Tbsp all-purpose flour (plain flour) to the pan.
  
• Blend the flour and butter until no more lumps. Keep stirring to avoid burning the roux.
  
• To the roux, gradually add 2 cups warm milk, a tiny bit at a time. Combine the roux and milk well, scraping the bottom of the pan, before adding more milk.
  
• Once blended well, season with freshly ground black pepper. Add ¼ cup reserved seafood sauce and keep stirring to combine with the béchamel sauce.
  
• Add 1 tsp soy sauce and mix well to combine. Keep stirring and cook on low heat until the desired consistency.
  

To Assemble and Broil

• When the sauce consistency thickens and you can draw a line on the bottom of the pan, add the seafood.
  
• Mix well and add the blanched broccoli.
  
• Pour the seafood mix and béchamel sauce on the butter rice in gratin dishes. Make sure each one gets all the different ingredients.
  
• Sprinkle with freshly grated Gruyere cheese and 2 Tbsp panko (Japanese breadcrumbs) for a crispy texture.
  
• Set the oven to broil (High) and preheat for 5 minutes. Put the gratin dishes in the oven and broil for 2–3 minutes until the cheese has melted and turned a golden color on top. Garnish with Italian parsley and serve warm.
  

To Store

• Keep the leftovers in an airtight container and store in the refrigerator for up to 3 days and in the freezer for a month.