Preheat the oven to 400°F / 204°C. Line a rimmed 13 × 18-inch / 33 × 46-cm baking sheet with parchment paper. On a lightly floured surface, unroll the thawed puff pastry and cut it into approximately 1-inch / 2.5-cm strips.
Wrap the pastry strips around the Brie in overlapping bands, leaving an opening for the eyes. Transfer the wrapped Brie to the parchment-lined baking sheet.
Whisk the egg with the milk and brush the mixture over the pastry. Bake for approximately 20 minutes, until the pastry is deeply golden and the Brie is warm and gooey.
Place the mini pepperoni pieces inside the sliced black olives to create eyes. Serve warm with crackers.