Prep time 20 minutes plus 30 minutes resting
Heat olive oil in a large frying pan on medium-high and cook the leek for 10 minutes or until soft and translucent.
Add the bacon and cook for another 5 minutes.
Now add the flour and mustard and cook for a few minutes stirring well so every piece of leek and bacon is coated with a little flour.
Pour in the stock and thyme and bring mixture to a bubble. Reduce heat and cook, stirring for 5 minutes or until mixture has thickened.
Remove from heat and stir through the cream.
Line a greased pie tin with flaky pastry and reserve and re-roll trimmed pastry for the lid.
Stir chicken through the cream sauce and then put both the chicken mixture and lined pie tin in the fridge to rest for 30 minutes.
Preheat oven to 200C
Place the chicken mixture into your lined pie tin. Gently place the 'lid' on top and poke a few holes in the top of the pastry to let steam escape.
For egg wash: beat egg and cream. Brush over the pie top.
Sprinkle with sesame seeds and either place in the fridge until needed (for up to 2 days) or bake straight away for 35-45 minutes or until golden.