Preheat your oven to 180°C / 160°C fan / 350°F / gas mark 4 and line a 2 lb loaf tin with greaseproof baking parchment.
Put the butter and medlar pulp into a large bowl. Using a wooden spoon, stir the ingredients together until there are no more lumps of butter.
Whisk in the sugar until smooth, then gradually incorporate the eggs until everything is combined.
Add the baking powder, self-raising flour, and salt. Whisk again until the mixture is smooth and lump-free.
Fold in the roughly chopped walnuts.
Spoon the mixture into the prepared loaf tin.
Bake for 20 minutes, then reduce the oven temperature to 170°C / 150° fan / 340°F / gas mark 3.
Cook for another 45 to 50 minutes until the loaf is brown on top and a skewer inserted into the centre comes out clean.
Rest the loaf in its tin for 15 minutes before removing it to a wire cake rack to cool down completely.
