1. Preheat the oven to 220°C/ 200°C fan and line 2 baking sheets. Unroll the puff pastry sheet with a thin end toward you, and brush it lightly with water. Grind black pepper over the pastry sheet until it’s covered with a thin, even layer, then sprinkle over a small amount of salt.
2. To shape the palmiers, fold one long edge in by a quarter, then do the same on the other side. Now fold both edges in to meet in the middle, leaving a 1 centimeter gap. Now fold one half over the other without pressing down. Gently slice 1 centimeter slices and lay them cut side up, placing them down so each is in ‘V’ shape, well spaced on a lined baking sheet.
3. Bake in the hot oven for 10 minutes then turn over and bake for another 5 minutes. Transfer to a wire rack and leave to cool.
4. Slice the top off the brie and place it on a serving dish. Sprinkle the caster sugar over the top of the brie, making sure all of the cheese is well covered - any protruding bits of cheese will burn - then use a small blowtorch to caramelise it. Serve immediately, with the black pepper palmiers for dipping.