1. Heat the oven to 210°C, fan forced.
2. Cut 2 discs of puff pastry, 18cm and 20cm in diameter, using different size bowls as a guide.
3. Place the 18cm disc onto a lined baking tray.
4. Cut the Castello Pink Peppercorn Brie in half, horizontally, so that you have 2 semi-circles.
5. Place the 2 pieces of brie in the centre of the pastry disc to form a circle.
6. Spoon the caramelised onions over the brie.
7. Whisk the egg and milk together to create an egg wash.
8. Brush the sides of the brie and the exposed pastry with egg wash.
9. Place the 20cm pastry disc on top, gently pressing the pastry into the sides of the brie and down onto the pastry base.
10. Slightly trim the excess pastry around the edge.
11. Brush with egg wash before placing into the refrigerator for 5 minutes.
12. Using a sharp knife, cut a small hole in the centre of the pastry. Then score the top of the pastry with lines from the centre to the outer edge.
13. Bake in the pre-heated oven for approximately 25-30 minutes, until the pastry has risen and is golden in colour.