Coarsely chop 125 g walnuts and roast them in a pan without fat until golden brown, take them out. Melt butter. Mix semolina, flour, baking powder and vanillin sugar.
Mix yoghurt and 350 g sugar. Stir in butter, semolina mixture and roasted walnuts and let it swell for about 15 minutes. In the meantime grease a baking tray (32 x 39 cm).
Whisk the semolina mixture with the whisk of the hand mixer for 2-3 minutes, place on a baking tray and smooth down. Bake in the preheated oven (electric range: 200 °C/ convection oven: 175 °C/ gas: level 3) for 20-30 minutes until golden brown.
In the meantime, caramelise 150 g sugar with a little water in a pot until golden brown. Wash the oranges hot, grate them dry and tear off the zest. Halve the oranges and squeeze them. Deglaze the caramel with orange juice and boil it down for 7-10 minutes over a low heat to a thick, syrupy consistency.
Finally fold in the orange zest and let it cool down.
Take out the cake, drizzle with orange syrup while still hot (possibly use the remaining orange juice for other purposes) and leave to stand overnight. Decorate with remaining walnuts
12 hours waiting time