Heat a frying pan over a low heat. Add the sunflower seeds and dry fry for 1-2 minutes, or until toasted. Stir in the soy sauce and cook until evaporated. Remove the seeds and set aside.
Heat the butter, sugars, salt and 2 tablespoons water in a saucepan over a low heat until the butter has melted and the sugar has dissolved.
Bring the mixture to the boil, then reduce the heat to moderate and continue to cook until the temperature reaches 150C. Remove the pan from the heat and stir in the lavender flowers, then set aside to cool slightly.
Pour the brittle mixture into silicone ice-cube trays, then sprinkle over the sunflower seeds. Set aside to harden, then remove from the moulds and serve.