If the sesame seeds aren’t already toasted, heat a dry frying pan over a low to medium heat. Add the white and black sesame seeds and toast for 3–5 minutes, stirring constantly, until fragrant and lightly golden. Transfer to a plate and set aside to cool.
Tear the nori sheets into small, flaky pieces by hand or with kitchen scissors.
In a medium bowl, combine the cooled sesame seeds, nori flakes, bonito flakes, caster sugar and fine sea salt. Stir until evenly mixed.
Transfer the furikake to an airtight jar and store in a cool, dry cupboard for up to three weeks.