Mix the gluten free flour, a pinch of salt and the lactose free butter in a bowl, then stir in the cheese. Blend 2 tbsp cold water with the mustard and stir in. Form into a dough. Wrap and chill for 30 minutes.Fry the chicken in the hot lactose free butter and oil for 5 minutes until golden. Add the stock, bring to the boil then cover and simmer gently for 15 minutes.
Preheat the oven to 200C/gas 6/fan 180C. Transfer the chicken to a 1.2 litre pie dish with a slotted spoon – leave the stock in the pan. Make a paste with the flour and 1 tbsp cold water. Thin with 2 tbsp stock then add to the pan and stir on the heat non-stop until thickened.
Take off the heat, stir in the lactose free cream and chives, season and pour over the chicken. Cool.Roll out the pastry between 2 pieces of cling film until just larger than the dish. Remove the top piece of film and lift the pastry onto a rolling pin with the cling film underneath. Lay pastry-side down over the filling. Peel away the film, then trim around the rim. Make a small hole in the centre. Brush the pastry with lactose free milk. Bake for 25-30 minutes until golden.
