Mushroom, mustard and tarragon bakes

Method

1. Chop the mushrooms into 1cm thick slices and put a large frying pan over a high heat. Once smoking hot, add a large knob of butter, then the mushrooms and fry for a few minutes, tossing the pan occasionally, until cooked through. Season with salt and pepper, then stir in the chopped tarragon and remove from the heat.
2. Melt the 25g butter in a medium pan, then stir in the flour to create a roux, cooking for a minute or two to remove the raw floury taste. Pour in a small amount of the hot milk while whisking continuously to incorporate, then keep adding and whisking until all the milk has been used and you have a smooth sauce. Stir in the tarragon mushrooms and the mustard, then season with salt, pepper and the cider vinegar. Taste to check the seasoning, then leave to cool completely – spreading the mixture out on a tray or plate will speed up the cooling process.
3. Once the filling is completely cool, un-roll the pastry with a long side nearest you (leaving it on the paper it comes with), then cut in half widthways so you have 2 smaller compact rectangles with a short side nearest you. Divide the filling between the bottom halves of each sheet, leaving a 1.5cm border. Egg wash the borders, then fold down the top half to cover and use a fork to crimp around the edges. Carefully move the bakes apart a few centimetres from each other as they will expand during baking. Pierce 2 holes in the centre of each bake, then lightly drag a fork over the top to create a diagonal line pattern over the top. Brush with more egg, then transfer them (still on the baking paper the pastry came in) onto a tray and put in the fridge to chill for at least 10 minutes.
4. Heat the oven to 200ºC fan/gas 8. Cook the mushroom bakes for 20-25 minutes until puffed up, golden and crisp on the bottom. Serve hot or at room temperature; they could even be cooled and taken on a picnic.