Preheat the oven to 200c / gas 6.

Roll out the puff pastry to 5mm thick. Cut into rectangles around 9 x 12cm.

Score the edges of the puff pastry rectangles to leave a 1cm border.

Lay the rectangles on baking sheets lined with non-stick baking parchment paper.

Spread heaped teaspoons of black olive tapenade on each rectangle leaving the borders clean.

Lay slices of portobello mushroom on the tapenade, drizzle with oil and scatter with chilli flakes if desired.

Brush beaten egg on the pastry borders. Bake for 12-15 minutes until puffed up and golden brown.

Can be served immediately or cool and box them up for your packed lunch or picnic.