Coarsely dice the fat. Knead with flour, hazelnuts, 80 g sugar and egg to a smooth dough. Cover and put in a cool place for about 30 minutes. Roll out the dough on a floured work surface to a thickness of about 4 mm. Grease a tart tin (approx. 23 cm Ø) and line with the dough. Bake in the preheated oven (electric: 200 °C/ gas: level 3) on the lower rack for about 20 minutes. Remove from the oven, allow to cool for approx. 20 minutes and take out of the tin.
Caramelise the remaining sugar bit by bit in a pan. Deglaze with 100 ml water and let it boil down to a thick consistency. Spread the nuts on the tart and pour the caramel over them. Let it cool down for about 20 minutes. Results in about 8 pieces. Serve with vanilla ice cream seasoned with grated nutmeg