Melt butter in a large fry pan over medium heat. Sprinkle with flour and cook, stir regularly for about 5 minutes, until golden brown. While stirring, slowly add chicken stock and reserved pan juices and the thyme. Bring to the boil then reduce heat, keep stirring until it thickens, roughly 10 minutes. Finally, remove from heat. Discard the thyme sprigs and stir in salt and pepper to taste. Serve on top of the hot turkey roulade.