Heat oven to 180C/160C fan/gas 4. Put the hazelnuts in a food processor and whizz until finely ground. Add the flour, eggs, extra yolks, sugar, milk, cream and vanilla and whizz until you have a smooth batter.
Halve, core and slice the pears (you can peel them first if you like, but I usually don’t). Arrange the pear slices in a 26 x 33cm ceramic, cast iron or copper gratin dish, then pour in the batter. Bake for 30-35 mins, or until the batter is set in the centre, golden and slightly souffléd.
For the topping, toast the hazelnuts in a dry frying pan (keep a close eye on them – they can go from toasted to burnt very quickly), then roughly chop them so you’re left with a mixture of halved and more finely chopped nuts. Scatter over the clafoutis, then sieve a little icing sugar over the top. Leave to sit for 10-15 mins (the clafoutis will deflate a little). Serve warm with crème fraîche or pouring cream.