Preheat the oven to 180°C (350°F) and line a baking tray with parchment paper.
In a bowl, cream together the butter, brown sugar, and golden syrup until smooth.
Add the vanilla extract and mix well.
Sift in the flour and baking powder, then knead to form a soft dough.
Roll the dough into small balls (about 2–3 cm in diameter) and flatten slightly with a fork.
Place on the prepared baking tray, leaving space between each biscuit.
Bake for 12–15 minutes until golden brown. Remove and let cool completely.
While the biscuits cool, melt the chocolate, butter, and golden syrup together over a double boiler or in short bursts in the microwave, stirring until smooth.
Once the biscuits are cooled, spread a small amount of chocolate mixture on the underside of one biscuit and sandwich it with another biscuit to make a pair.
Allow the chocolate to set at room temperature or refrigerate for faster setting.