300²µ/10½´Ç³ú chestnut mushrooms, trimmed
2 red onions, thinly sliced
2 tbsp thyme leaves
600g/1lb 5oz plain flour
2 tsp soft brown sugar
pinch salt
1 tbsp sesame seeds
1 tbsp sherry vinegar
1 tbsp sunflower oil
300²µ/10½´Ç³ú butter, 100²µ/3½´Ç³ú chilled and cut into cubes, 200g/7oz frozen
25g/1oz unsalted butter
1 free-range egg, beaten, to glaze
100²µ/3½´Ç³ú black pudding, cut into 2cm/1in pieces
300²µ/10½´Ç³ú good-quality sausage meat