Simmer the Sweet Soy Glaze
In a small saucepan, combine 100ml of soy sauce, 100g of brown sugar, 2 tablespoons of rice vinegar, 1 teaspoon of sesame oil, 1 teaspoon of finely grated fresh ginger, and 1 teaspoon of finely grated fresh garlic.
Place the pan over medium heat and bring it to a gentle simmer, stirring occasionally to ensure the brown sugar completely dissolves.
Let the mixture bubble gently uncovered for 6 to 8 minutes until it reduces to a glossy, maple syrup consistency. Set it aside to cool slightly and thicken up.
Precision Slice the Salmon
Using a very sharp knife, slice your sashimi-grade salmon loin into thin, elegant strips (similar to sashimi or carpaccio thickness). Arrange the salmon slices on a heatproof serving plate, overlapping them slightly to create a beautiful presentation.
Glaze and Torch
Spoon the cooled sweet soy glaze generously over the top of the salmon slices, ensuring each piece is lightly coated.
Ignite your kitchen blowtorch. Holding the torch at a safe distance and keeping the flame moving constantly in a steady sweeping motion, flash it across the salmon. Watch closely as the sweet soy glaze bubbles furiously and darkens, and the edges of the fish just begin to sear and caramelize.
Garnish and Serve Immediately
Immediately scatter a generous shower of finely sliced spring onions (or chives) and a sprinkle of toasted sesame seeds over the glistening, caramelized salmon. Serve straight away while the surface glaze is warm and the center remains perfectly tender.