Preheat oven to 160°F. Roast the black sesame seeds for 10 to 15 minutes, until the sesame turns fragrant. (It’s hard to tell exactly when black sesame is well toasted, so you can put a little pinch of white sesame on a separate tray and roast that in the oven together with the black sesame, and when the white sesame is nice and golden-brown, you’ll know your black sesame is done too.)

Put the caster sugar, treacle, salt, and water into a medium pot or pan, and bring it to a boil. Keep the syrup on a steady simmer, letting it bubble and heat up until it reaches 125°C (‘hard ball’ stage). (If you don’t have a sugar thermometer, you can spoon out a little syrup into a bowl of cold water, and if it turns into a rough ball of sugar, it’s done.)

When the sugar syrup is done, take it off the heat, and quickly pour in the toasted sesame seeds. Give it a stir so the sugar is spread evenly, then immediately pour everything out onto a silicon mat or a sheet of parchment paper. Place another mat or parchment paper on top, and roll it out firmly with a rolling pin until it’s about 0.5cm thick all over. (You can go thinner, but I like my brittle to be a bit more sizeable so you can munch on it like a biscuit.)

Once it’s rolled out, let it cool slightly, and cut it into strips with a heavy knife. (You can cut them into square, rectangles, or do as I did and make them into diamonds. Or you can let your imagination run wild and cut out stars, even!) Store in an airtight container if not having immediately. It keeps well for up to a week.