In a substantial skillet, soften the margarine and cook the leeks, secured, for 10 mins until extremely delicate. Expel from the warmth and mix through the cheddar sauce, chives, chicken, milk and mustard. Blend well and spoon into little dishes or ramekins.
Un-roll the cake on a daintily floured surface. Utilize a saucer to cut circles for the pie tops. Spot to finish everything, trim to fit, crease the edges and brush with egg to coat. Wrap firmly in stick film and stop for as long as 2 months.
To cook from solidified, heat stove to 220C/200C fan/gas 7. Evacuate the stick film, spread with foil and put on a preparing plate amidst the stove. Prepare for 15 mins, at that point lessen the temperature to 190C/170C fan/gas 5 and heat for a further 45 mins, evacuating the foil for the last 30 mins. Present with green vegetables.
To cook from new, heat broiler to 190C/170C fan/gas 5. Cook for 45 mins, until the baked good is brilliant and puffed, and the filling is sizzling.