Preheat your oven to 170deg (fan) 150deg (conventional).
Line a 20cm x 20 cm baking tray with baking parchment, cut slits in each corner so it fits neatly.
Melt your butter in a large pan over a low heat.
Once melted add your sugar. and golden syrup. Once the sugar has dissolved remove from the heat and stir in the oats.
Give the entire mixture a really good stir so that all of the oats are coated.
Bake in the oven for 20 minutes, the edges should be starting to brown but the middle should still be soft and wobbly.
When the flapjacks are cold, remove from the tin and slice your flapjack into 16 squares with a sharp knife.