To make the pastry, sift the flour, add the butter and rub it in. Sift in the icing sugar and stir in the egg yolk mixed with cold water.
Mix to a dough, then knead on a surface until smooth. Roll out a circle that’s the same size as the tin. Wrap the pastry in cling film and chill until ready to use.
Heat the oven to 180°C. Melt the butter and brush a little over the inside of the cake tin. Line the base of the tin with grease proof paper and brush it with the rest of the melted butter. Sprinkle brown sugar over evenly and press it down.
Peel, core and thinly slice the pears. Arrange them, hollow-side up, pushing the slices apart a little, on the brown sugar. Place the pastry over the top and press it down. Bake for 35-40 mins until crisp and golden brown.
Cool for 5 minutes, then turn out on to a serving plate. Serve tart warm with custard or crème fraîche.