Preheat the oven to 180°C (355°F). Place the ricotta, parmesan and eggs in a bowl and whisk until smooth. Roll out the pastry on a lightly floured surface until 3 mm (1/8 inch) thick. Cut into 4 x 15 cm (6 inch) squares and place on baking trays lined with non-stick baking paper. Spread the ricotta mixture over the pastry squares leaving a 2 cm (3/4 inch) border. Place the leek on top of the ricotta mixture and brush with the butter. Sprinkle with the thyme, salt, and pepper and bake for 25–30 m