Carefully mix the different types of flour, the cocoa powder and a pinch of salt together on your work surface; then pile the mixture up and form a “well” in the middle. Put into it 75 g of butter (previously kept out of the fridge for at least 20 minutes) cut in pieces and, a little at a time, pour in approximately 150 ml of cold water, mixing quickly and kneading until you have a smooth, soft ball of dough. Cover it with cling film and put it in the fridge for about half an hour. In the meanwhile, peel the pears, remove their cores, cut each fruit into 8 segments and sprinkle with lemon juice. Put a heavy-bottomed frying pan on the stove, over a low heat, with 30 g of butter cut into pieces, the sugar and the pear segments. Cook for 10 minutes with the lid on, then take it off, turn up the heat and finish cooking (take care, the pieces of pear should caramelise but not disintegrate). Remove from the heat and leave to cool down. Arrange the slices of fruit in a well-buttered, 24 cm round cake tin; start from the outside and place them side by side in 2 concentric circles, then pour their cooking juices over them. Now take the ball of dough out of the fridge and roll it out between 2 sheets of greaseproof paper, using a rolling pin, to a thickness of approximately 3 mm. Remove the upper sheet of paper and, using the sheet underneath to help you, turn the disc of dough over on top of the slices of pear. Press it down with your hands, including around the edge. Prick the surface here and there with a fork and bake in a preheated oven, at 190 °C, for 30-35 minutes. When it’s cooked, take the tarte tatin out of the oven and leave to rest for 10-15 minutes.
In the meanwhile, put a small, heavy-bottomed saucepan on the stove with the milk and hazelnut butter; bring to the boil stirring frequently, add the chopped dark chocolate, remove from the heat and stir until you have a smooth, shiny sauce. Now run the blade of a knife around the edge of the cake tin to loosen the tarte tatin, place a round plate on top and turn everything over so it comes out. Drizzle the sauce you prepared over the surface and sprinkle with the coarsely chopped hazelnuts. 

This delicious, rich – gluten free! – dessert is similar to the classic French tarte tatin, but with different ingredients.