01 -
Heat the oven to 350°F (180°C). Line an 8-inch (20 cm) square baking tin with parchment paper, leaving overhang on two sides.
02 -
Add the butter, brown sugar, golden syrup, and salt to a large saucepan. Warm over low heat, stirring often, until melted and smooth. Do not let it boil.
03 -
Remove the pan from the heat. Stir in the vanilla if using, then add the oats and mix until they are evenly coated.
04 -
Scrape the oat mixture into the prepared tin. Press it firmly into an even layer, packing the corners well with the back of a spoon.
05 -
Bake for 18-22 minutes, until the edges are golden and the center looks set but still slightly soft. For chewier bars, avoid deep browning.
06 -
Let the flapjack cool in the tin for 10 minutes, then score into 16 bars. Cool completely in the tin before lifting out and slicing through the marks.