300驳/10陆辞锄 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
300驳/10陆辞锄 butter, 100驳/3陆辞锄 chilled and cut into cubes, 200g/7oz frozen
25g/1oz unsalted butter
1 free-range egg, beaten, to glaze
100驳/3陆辞锄 black pudding, cut into 2cm/1in pieces
300驳/10陆辞锄 good-quality sausage meat