Gluten free chicken and leek pies

Pie filling

• 800 g water
• 1 tbsp Chicken stock paste (see Tips)
• 500 g leeks ; green part cut into pieces and white part cut into rounds (1 cm) and reserved
• 1 carrot, cut into pieces
• 2 sprigs fresh flat-leaf parsley, leaves only
• ½ tsp black peppercorns
• 1 dried bay leaf
• 700 g skinless chicken thigh fillets
• 60 g salted butter
• 2 sprigs fresh thyme, leaves only
• ¼ tsp salt
• ¼ tsp ground black pepper
• 200 g pouring (whipping) cream
• 30 g gluten free cornflour

Pastry

• 50 g cheddar cheese (mature)
• 400 g gluten free flour mix (see Tips)
• 200 g unsalted butter
• 1 tsp xanthan gum
• 1 tsp salt
• 1 egg
• 40 g wholegrain mustard (gluten free)
• 3 tbsp water
• arrowroot flour, for dusting
• 1 egg yolk