Pare apples, halve and discard core with seeds, make X cuts on sides. Whisk butter with sugar and vanilla sugar until of a smooth light consistence. While keep whisking, gradually mix in eggs. Sift flour with baking powder, combine with egg mix, add nuts and mix. Line the form with parchment paper, grease sides.

Put the dough in the form, arrange apple halves cut side down and bake 45 minutes at 347 °F (175 °C).