Preheat your oven to 180℃ (or 160℃ for fan ovens) and line an 8x8 tin with baking paper.
Melt the butter, sugar and golden syrup together over low heat.
In a large bowl, mix the oats and cocoa powder together. Then pour in the wet mixture and the orange extract. Mix well.
Press the mixture firmly into your tin and bake for around 20 minutes. The flapjacks should be firm at the edges and slightly wobbly in the middle. They'll become firmer as they cool.
Let them cool in the tin for around 5 minutes then use a knife to gently score lines where you plan to cut them. This will help you get cleaner slices.
Leave the flapjacks to cool completely, around 3-4 hours, then remove them from the tin.
Melt the chocolate and stir the orange extract in. Drizzle this over the flapjack and stick a mini Terry's Chocolate Orange segment onto each slice, using your score marks as a guide.
Let the chocolate topping set then cut your flapjack into slices and enjoy!