Pre heat oven to 190C, grease an oven proof dish with a little of the butter. Melt the rest in a pan and cook the shallot over a low heat until soft. Tip into a bowl and mix with the thyme, lemon zest and breadcrumbs. Gently stir in 75g raspberries and the egg yolk. Season well.
Using a sharp knife make a cut in the side of each chicken to make a pocket. Fill the pocket with the stuffing and reshape, tie up with string or pin edges together with cocktail sticks. Put in the oven proof dish skin side up and cook for 30 mins. Remove string/cocktail sticks.
Meanwhile, simmer the rest of the raspberries in a small pan with 4 tbsp water for 2 mins then pass through a sieve to remove the seeds. Return to the pan and add the vinegar, redcurrant jelly and sweet chilli sauce. Heat stirring until the jelly melts. Mix cornflour with 2 tbsp water and then stir in. Heat stirring until boiling and thickened. Serve with the chicken.