Cut 100 g tuna steak into cubes and place them in a bowl with 3 tbsp Japanese soy sauce (koikuchi shoyu), cover and store in the refrigerator for 30 minutes. Remove the shells of 10 large shrimp and set aside both for later. Thinly slice 1 onion.
Start heating a pan on medium with 1 tbsp olive oil. Once hot, add the sliced onions. Stir every few minutes to encourage even browning.
Add a sprinkle of salt and mix well. Reduce the heat to low and cook for 20-30 minutes or until deep brown and caramelized. Stir occasionally to prevent burning and add a sprinkle of water if it starts to stick.
Devein the shrimp and place them in a bowl. Rub with 2 pinches salt and 1 tsp cornstarch, then set aside for 5 minutes.
While you wait, heat a wok, pot or large frying pan on low. Add 2 tbsp olive oil and the shrimp shells. Leave to gently infuse for 10-15 minutes on the lowest heat, then remove the shells.
Wash the shrimp with fresh water and pat them dry with kitchen paper.
Use any waiting time to cut the vegetables and measure the rest of the ingredients. Once all of these elements are complete, move onto the next part.
Part 2 (Browning Ingredients - 5 minutes)
Take the pot with the shrimp infused oil and increase the heat to medium. Remove the tuna from the soy sauce and add it to the pan, save the leftover soy sauce for later. Add the shrimp, 100 g scallops, 2 potatoes and 1 carrot and cook until the seafood starts to change color and looks opaque.
Once done, transfer the seafood and vegetables to a plate for later. We will reuse the pot in the next steps.
Part 3 (Roux - 10 minutes)
Return the pot to the heat on medium-low and melt 2 tbsp butter. Add 3 cloves garlic and 1 tbsp ginger root (finely diced or minced) and fry for about 1 minute or until fragrant.
Add the caramelized onions from earlier along with 2 ½ tbsp curry powder, 3 tbsp all-purpose flour and 1 tsp squid ink.
Mix thoroughly until it forms a thick paste.
Part 4 (Curry & Secret Ingredients - 25 minutes)
Gradually add 850 ml dashi stock while stirring continuously to smooth out any lumps. Once smooth, add the seafood and vegetables back into the pot along with 1 bay leaf. Simmer for 15 minutes.
Add you choice of secret ingredients for extra depth. I add 2 tbsp white wine, ½ tsp garam masala, ½ tsp instant coffee powder, ½ tbsp honey, ½ tbsp blueberry jam and ½ tbsp Worcestershire sauce.
Simmer for another 5-10 minutes or until thickened to your liking.