Mix the speculoos finely in a universal chopper. Knead the crumbs with 125 g sugar, flour, 250 g butter in flakes, cinnamon, honey and 1 egg first with the dough hooks of the hand mixer, then with your hands to a dough.
Press the dough as a base onto a greased, floured baking tray (approx. 36 x 41 cm).
Coarsely chop the walnut kernels. Cream 250 g butter, 1 packet vanilla sugar and 250 g sugar with the whisks of the hand mixer. Separate 6 eggs, stir egg yolks one after the other into the butter-sugar mixture.
Stir in milk, 1/2 sachet pudding powder, baking powder, poppy seeds, walnuts, breadcrumbs, sultanas, candied orange peel and almond liqueur. Beat the egg white with the whisk of the hand mixer until stiff, then carefully stir into the poppy seed mixture.
Cream 175 g butter, 75 g sugar, salt and 1 packet of vanilla sugar with the whisks of the hand mixer. Separate 3 eggs, stir egg yolks one after the other into the butter-sugar mixture. Stir in 2 packets of custard powder and quark.
Whisk the egg whites with the whisk of the hand mixer until stiff, adding 75 g sugar. Carefully fold the beaten egg whites into the curd mixture.
Spread the poppy seed mixture on the speculoos base. Spread the curd mixture on top, swirl with a fork and smooth it down. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for approx. 1 hour.
Take out and let it cool down on a cake rack. Dust with icing sugar if necessary.