Rinse the Japanese short-grain rice thoroughly. Place the 500g (2.5 cups) of rice in a bowl and add cold water. Swirl the rice gently with your hand, then drain the cloudy water. Repeat this rinsing process 4-5 times, or until the water runs mostly clear. This step removes excess starch, preventing the rice from becoming gummy.

Cook the rice. Transfer the rinsed rice to a rice cooker or a heavy-bottomed pot. Add 550ml (2.3 cups) of water. If using a rice cooker, select the standard cooking setting. If using a pot, bring the water to a boil over medium-high heat, then reduce the heat to low, cover tightly, and simmer for 15 minutes. After simmering, turn off the heat and let the rice steam, covered, for another 10-15 minutes. Do not lift the lid during this steaming period.

Season the rice. Once the rice is cooked and steamed, gently fluff it with a rice paddle or a wooden spoon. If using, drizzle 1 tbsp (15ml) of rice vinegar over the rice and sprinkle with 1 tsp (5g) of salt. Gently fold these ingredients into the rice, taking care not to mash the grains. Let the rice cool slightly until it's comfortable to handle, but still warm.

Prepare the Tuna Mayo filling. In a small bowl, combine the drained canned tuna (approx. 150g / 5.3 oz), 2 tbsp (30g) of mayonnaise, a pinch of salt, and a pinch of black pepper. Mix well until evenly combined. Taste and adjust seasoning if necessary.

Prepare the Salmon filling. In another small bowl, combine the flaked cooked salmon (approx. 100g / 3.5 oz) with 1 tsp (5ml) of soy sauce and optional 0.5 tsp (2.5ml) of mirin. Mix gently to combine, ensuring the salmon is evenly coated without becoming mushy.

Prepare your hands for shaping. Fill a small bowl with water and stir in 1 tsp (5g) of salt. This salted water will prevent the rice from sticking to your hands and seasons the outside of the onigiri.

Shape the onigiri. Take a portion of warm rice, about 1/2 cup or roughly 150g (5.3 oz), into your wet hands. Gently flatten the rice in your palm. Place about 1 tablespoon of your chosen filling (tuna mayo or salmon) in the center of the flattened rice.

Enclose the filling. Carefully bring the edges of the rice up and around the filling, ensuring it is completely enclosed. Gently press and mold the rice into a triangular shape. Use your palms and fingers to form the corners and smooth the surfaces. Rotate the onigiri as you press, re-wetting your hands as needed. Aim for a firm but not overly compressed shape, about 5-7cm (2-3 inches) in size.

Repeat shaping. Continue this process for the remaining rice and fillings, making approximately 8 onigiri. You can alternate between fillings or make all of one kind.

Wrap with nori. Take a strip of nori seaweed (approx. 2.5cm / 1 inch wide and 10cm / 4 inches long) and wrap it around one corner of the onigiri. The nori acts as a handle and adds a savory flavor. You can moisten the end of the nori slightly with water to help it stick.

Serve. Onigiri are best enjoyed at room temperature or slightly warm. They are perfect for lunchboxes, picnics, or as a satisfying snack. Store any uneaten onigiri in an airtight container at room temperature for up to 12 hours. Avoid refrigerating, as it can make the rice hard.