First, make the filling by heating the olive oil in a large frying pan, add 1 tablespoon of butter and fry the leeks and shallot until they soften (about 5 minutes).

Add the mushrooms and the remaining butter and garlic and cook for about 5 minutes and until all the water has evaporated.  Add the herbs and cream and carry on cooking until it thickens again.

Add the Parmesan cheese and turn off the heat allowing the cheese to melt into the mixture which should be fairly thick. Add salt and pepper, test, and adjust if necessary. Allow the mix to cool slightly, making it easier to handle.

Preheat the oven to 180 C/350F  and work fairly quickly to unroll 2 sheets of phyllo off the roll.  

Flip one half of the phyllo sheet back and brush the entire surface with the melted butter/olive oil.  Fold the top phyllo sheet back over the buttered surface and repeat with the other half of the sheet.  

Cut the sheet in half down the center and then each half into half again.  Spoon a dessert spoon of mix into the bottom corner and roll it up into triangles.

If you need further details or alternative instructions on this, you can check out my previous post on making spinach and feta pies.

*Remember to roll the remaining phyllo up tightly, put it back in its plastic bag and box and refreeze.

Arrange the pies next to each like a puzzle so they fit on one baking tray which is lined with silicone paper or baking paper, brush the tops with the olive oil / melted butter mix and bake in the oven for 20 - 25 minutes until golden brown.

This filling would work well on toasted bruschetta or open phyllo tart cases.  You could replace the Parmesan cheese with Gruyere or feta.