Preheat oven to 220°C. Heat the oil in a large pan over a high heat. Add the sliced leeks and stir about until softened slightly, then tip in the pancetta lardons and continue to cook for a couple of moments until the pancetta becomes paler in colour.
Meanwhile, cut the chicken thighs into small bitesize pieces. Add them to the pan then discard the cutting board and wash hands.
Stir in the butter and when melted add the flour and thyme. Stir everything about in the pan until a floury paste coats everything in the pan and the flour has cooked out a bit.
Add the red vermouth, chicken stock and petit pois. When it begins to bubble reduce the heat and allow to simmer, while you get on with the pastry.
To make the topping, unroll the sheet of pastry and place one of the bowls the pie is going to be cooked on top of the pastry upside down and cut around the rim, use the cut out disc of pastry as a guide to out the other three lids. Then cut 4 strips of pastry approx 1 1/2 cm wide that will fit around the entire rim of the bowl.
Dabble your finger in some water and wet the rim of the bowl to help the strips of pastry stick to the bowl. Allow a little of the pastry to stick up over the rim, fold this flap over the rim so the lid has pastry to stick to.
You can at this stage check your chicken is fully cooked and allow to cool or if impatient like me ladle the hot pie filling into the bowls filling them a bout 2/3 full. (if you use hot pie filling the pastry may sag a little in the oven but, will still be perfectly fine) Then place the lids on and press all around the edges with you fingers to seal. Make 2 or 3 slits in the top of each to allow steam to escape before baking in the oven for 20 minutes until the pastry has puffed up and become golden brown.