The flavor of the black sesame seeds comes through big and bold in this brittle, their slight bitterness tempered by the sweetness of the caramel. Best of all, this homemade candy is just a little nutty and a little funky—but always sweet. —Jun
Preheat oven to 320°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 300°F ("hard crack" 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 solid 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 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 1/4 to 1/2–inch 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, cut it into 2-inch squares with a knife. If you prefer, you can also just let it cool completely and then smash it up with a mallet to get shards that are irregular and edgy (in both senses of the word).
When the brittle is completely cooled, you can eat it immediately. Or if you’re saving it for later, store in an airtight container so it doesn’t lose its snap.