1. With the rack in the middle position, preheat the oven to 400°F (200°C). Line a baking sheet with a silicone mat or parchment paper.
2. On a work surface, cut the puff pastry into twenty five 2-inch (5 cm) squares. Place the squares on the baking sheet. Cover with another sheet of parchment paper and another baking sheet.
3. Bake for 20 minutes. Remove the top baking sheet and piece of parchment paper. Let the pastry squares cool.
4. Brush the pastry squares with the mayonnaise and sprinkle with the cheese. Bake for 3 to 4 minutes or until the cheese has melted.
5. Remove the baking sheet from the oven. Top each pastry square with pieces of smoked meat, mustard and gherkins.

Chef’s tip

For an even simpler version, use rye bread croutons instead of puff pastry.