Mix nuts, flour and icing sugar. Cut 75 g butter into cubes and mix until the mixture is finely crumbly. Add egg yolks and knead to a soft dough. If necessary add 2-3 tbsp. cold water.
Cover the dough and let it rest for about 15 minutes. Roll out to a circle (approx. 25 cm Ø) on a floured work surface, place on a plate and chill for approx. 30 minutes.
Heat 75 g butter and sugar in a pan with an ovenproof handle (23 cm Ø) and caramelise over medium heat while stirring occasionally. Remove from the stove. Clean, wash, halve and stone the plums.
Place in the pan with the cut side facing upwards. Wash the rosemary, shake dry and scrape the needles off the twigs. Chop the needles finely and sprinkle over the plums.
Place the dough on top, pressing the edge of the dough downwards into the pan. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) for 25-30 minutes until the tart is crispy and golden brown.
Leave to cool in the pan for about 5 minutes, then turn out onto a serving dish.