to medium-low. cook onion in pan, stirring often, for 3-4 minutes or until soft. add to the dish. cover and bake for 40 minutes.
meanwhile, place the cider, stock, vinegar and thyme in a small saucepan over medium-high heat. bring to the boil. combine the flour and a little water in a small bowl. gradually add the flour mixture to the cider mixture, whisking constantly, until well combined. stir until thick. simmer for 3 minutes.
heat remaining butter in the frying pan over medium heat. add the extra apple and cook for 3-4 minutes each side or until golden.
add the sour cream to the cider mixture and stir over medium heat for 