Melt the plant-based butter in a wide deep pan and fry the leeks for about 5 minutes or until starting to soften.
Squeeze the Kallo Organic Vegetable Stock Paste into the pan and mix well.
Stir in the flour and mix well to coat the leeks, then gradually add 500ml water.
Heat, stirring, until thickened then add in the asparagus, mustard, peas and Merchant Gourmet Chestnuts, mix well and season.
Spoon into a deep pie dish and let cool. Unroll the pastry and use it to top the pie, trimming and crimping the edges. Bake for 25 minutes, or until the pastry is golden.
