Unroll pastry sheet or roll out pastry to a rectangle or square about the thickness of a £1 coin. Place on a baking sheet.
Preheat the oven to 200℃ (180℃ fan)/400°F/gas mark 6.
Score a 2cm/1in border around the edge of the pastry cutting about half way through the pastry. Gently score a diamond pattern on the border if desired.
Prick the centre of the pastry all over with a fork, then bake in the preheated oven for 10 minutes.
While the pastry is part baking, melt the butter with the oil and gently sauté the courgettes and leeks for about 5 minutes until just beginning to soften and colour.
Once the pastry is ready remove from the oven and carefully press down the centre of the pastry to form a pastry case. Spread the leeks and courgettes over the base and arrange the asparagus on top.
Place the ricotta in a bowl with the eggs and milk. Season with salt, pepper and a pinch of nutmeg. Beat together with a fork until well combined. Spoon over the vegetables and sprinkle the top with the grated parmesan.
Bake for 20-25 minutes until the filling is set and the top is just turning golden. Allow to cool for a few minutes before serving hot, or cool completely and serve cold.
Nutrition information is approximate and is meant as a guideline only. (It does not include seasoning with salt and pepper.)