Preheat the oven to 180°. Peel and core the pears, cutting them into quarters or sixths if they are large. As you go, rub them with the lemon halves to prevent browning.

Melt the butter in a large frypan over moderate to high heat. Add the caster sugar and stir for 1-2 minutes. Add the pears, coating them with the sugar and butter. Hopefully they all fit in one layer for you, otherwise turn them regularly. Let the pears cook and soften - as you do this, the sugar will start to caramelise.

Once the pears are just tender (a good way to test this is when you can spear them through with the tines of a fork and meet only a little resistance) and the sugar is caramelised, normally around 10-15 minutes, tip the pears and the leftover juices into a baking dish (about 1.5-2L) (NOTE: I have found that cast iron pans or oven proof frypans are ideal for cooking this crumble in as the pears continue to caramelise more than in a ceramic baking dish, but if you don’t have that option then a ceramic baking dish will still produce a delicious crumble!)

To make the crumble, rub the butter into the flour with your fingers or use a food processor, pulsing the mixture until it resembles coarse breadcrumbs.

Stir in the brown sugar and oats. Add the tablespoon of milk and shake until it forms gravel size lumps (you may need 2 tablespoons, it really depends on the softness of your butter etc). Stir through the chocolate and walnuts.

Tip the crumble mixture over the pears in a roughly even layer. Bake for 35-45 minutes or until lightly browned and crunchy on top. Baking times will vary slightly depending on what type of pan you use - a cast iron pan will cook much more quickly than a ceramic dish as it holds the heat better.

Dust with icing sugar and serve hot with ice cream