Ingredients
Method
1.Bring stock to the boil in small saucepan. Add chicken; return to the boil. Reduce heat; simmer, covered, about 10 minutes or until chicken is just cooked. Cool chicken in poaching liquid 10 minutes. Remove chicken; reserve ¼ cup of the poaching liquid (keep remainder for another use, or discard). Chop chicken finely.
2.Heat oil in medium saucepan; cook leek and celery, stirring, until leek softens. Add flour and half the thyme; cook, stirring, 1 minute. Gradually stir in reserved poaching liquid and cream; cook, stirring, until mixture boils and thickens. Stir in chicken and mustard. Cool 10 minutes.
3.Preheat oven to 220°C/425°F. Oil eight holes in each of two 12-hole patty pans.
4.Using 7.5cm (3-inch) cutter, cut 16 rounds from shortcrust pastry; press one round into each pan hole. Spoon 1 tablespoon of the chicken mixture into each pastry case.
5.Using 6cm (2½-inch) cutter, cut 16 rounds from puff pastry; top with puff pastry rounds. Brush with yolk; sprinkle with sesame seeds and remaining thyme. Cut two small slits in top of each pie.
6.Bake pies 20 minutes or until browned lightly.
