Steps

1. Defrost the frozen peeled shrimp. Prepare a saltwater solution by mixing water (not included in ingredients) and 1 tsp salt in a bowl until the salt dissolves. The salinity should be similar to seawater. This is the key! Defrosting in saltwater will result in plump, firm shrimp.
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2. Once the salt is dissolved, add the frozen peeled shrimp (120g) to the saltwater and let it thaw for 30 minutes to 1 hour.
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3. Bring water to a boil in a pot.
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4. Once boiling, add 1/2 tsp salt and cook the macaroni (50g) for 1 minute less than the time indicated on the package (e.g., if it says 9 minutes, cook for 8 minutes). This is the key! The macaroni will continue to cook in the sauce later, so it's best to cook it slightly al dente.
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5. After 8 minutes, turn off the heat and drain the macaroni.
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6. Drizzle a small amount of olive oil (not included in ingredients) over the drained macaroni and toss to coat. This is the key! Coating with olive oil immediately prevents the macaroni from sticking together.
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7. Cut off the core of the onion (1/2) and slice it thinly.
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8. Discard the saltwater used for defrosting the shrimp and rinse them once.
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9. After rinsing, thoroughly pat the shrimp dry with paper towels. This is the key! Any remaining moisture can leave a fishy odor, so be sure to dry them well.
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10. If there's a vein on the shrimp's back, make a shallow cut with a knife and remove the vein using a toothpick or similar tool.
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11. In a frying pan, melt half of the salted butter (20g), spreading it evenly.
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12. Once the butter has melted, add the sliced onion (1/2) and the dried peeled shrimp (120g).
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13. Season with salt and pepper (to taste), add 1 tbsp of Cooking Sake (Rice Wine), and stir-fry over medium heat. This is the key! Stirring the onions to separate them and cooking with sake helps to remove any fishy smell from the shrimp.
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14. Once the onions are softened, add the canned button mushrooms (50g) and stir-fry for about 1 minute.
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15. Turn off the heat and spread the ingredients evenly in the frying pan.
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16. Sift 2 tbsp of all-purpose flour over the ingredients and mix well to coat. This is the key! Always sift the flour while the heat is off. Adding it directly can cause lumps.
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17. Turn the heat to low-medium and cook the all-purpose flour for about 1 minute. Be careful not to burn it.
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18. Gradually add 500ml of milk, stirring well with the ingredients each time to incorporate. Keep the heat on medium. This is the key! Adding all the milk at once can cause lumps. Add the next portion of milk once the mixture starts to simmer.
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19. Add the remaining milk and 1.5 tsp of granulated consommé, then stir.
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20. Lightly season with salt and pepper (to taste) and heat while stirring until it comes to a simmer.
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21. Once simmering, add the cooked macaroni (50g) and simmer over low-medium heat for about 1 minute.
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22. Add the remaining salted butter and 0.5 tsp of Soy Sauce, stir until the butter is melted, then turn off the heat. This is the key! Adding butter and soy sauce at the end preserves their flavor.
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23. Transfer the gratin mixture to an oven-safe dish.
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24. Sprinkle the shredded melting cheese generously over the top.
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25. Bake in a toaster oven (set to the highest temperature or wattage) until the surface is golden brown and bubbly. Adjust baking time as needed. This is the key! If you don't have a toaster oven, bake in a preheated oven at 250°C (480°F) for 5-10 minutes.
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