Step 1 of 4

Melt, do not boil

Heat the oven to 355°F and line a 20 by 30cm pan. Melt the butter, sugar and syrup together in a large pan over a low heat, stirring until the sugar has dissolved, then take it off the heat and stir in the vanilla and salt.

— Let it bubble and you are making caramel, which sets hard. Warm enough to dissolve the sugar and no hotter is what keeps a flapjack chewy.