Pre-heat your oven to 180C Fan/400F/Gas Mark 6. You may need to take the pastry out of the fridge and let it come to room temperature before unrolling it
Roll the pastry out onto a baking tray, if it doesn't come with baking paper make sure the tray is lined with it. Prick the pastry with a fork, avoiding a 1cm border around the edge
Mix the ricotta, egg, italian hard cheese, salt, thyme and lemon together until they form a smooth paste
Spread the ricotta mixture over the puff pastry sheet, leaving a 1cm border around the edge
Arrange the asparagus neatly on top, trimming the ends if needed, and sprinkle over the frozen 'petit pois' peas. Drizzle or brush the olive oil over the asparagus
Use a pastry brush dipped in the milk to glaze the 1cm border
Bake the tart for around 20-25 minutes, until the pastry is golden and risen
Chop up the mint leaves and sprinkle them over the tart
Serve hot, or allow to cool to room temperature, then refrigerate for up to 2 days. You can re-heat the tart or serve it cold