Photograph: Tara Fisher
To make the custard, bring the milk to the boil in a small pan. Put the egg yolks in a medium-sized heatproof bowl, then gradually pour the hot milk over them, whisking constantly until combined. Pass through a sieve into a clean bowl. Gently melt the chocolate in a bowl set over a pan of barely simmering water, then remove from the heat and whisk in the custard base, a quarter at a time, until you have a rich chocolate cream. Cover and leave to cool, then chill.
Heat the oven to 190°C, fan 170°C, gas 5. Place the flour, cocoa, ground almonds, sugar and butter in a food processor and whiz until the mixture resembles fine crumbs. Transfer to a bowl and fold in the chocolate chips.
Peel, halve and core the pears, and arrange cut-side up in a medium roasting tin or baking dish. Scatter the crumble over the top and bake for 40 minutes. Leave to stand for 10-15 minutes. Serve with the chilled chocolate custard.
Note: this recipe contains partially cooked eggs.
Get ahead: make the custard the day before; chill. Prepare the crumble topping the day before; store in an airtight container in the fridge. The topping can also be frozen; defrost before using.
Kitchen secret: try a ginger-choc crumble topping, too – just substitute the cocoa for 1 tsp ground ginger.