Melt the butter and cook the finely chopped garlic until it softens, then add the mushrooms and cook for 10 - 12 minutes on a low heat until they're beginning to brown. Remove from the butter with a slotted spoon and rest on kitchen paper.

In the remaining butter, cook the very finely chopped leeks for 10 minutes until they soften.

In a clean pan, make a white sauce with butter, flour, mushroom powder and flavored milk. Season when thick.

Stir the garlic mushrooms and leeks into the white sauce.

Line picnic pie tins with hot water crust pastry. There is no need to blind bake. Fill with the mushrooms and leeks, leaving space for the lid. The filling will expand slightly, so don't overfill.

Add the lid and crimp. Bake at 400° F for 25 minutes or until golden brown.