Grind wheat and place in a suitable bowl with cocoa powder, powdered sugar, vegetable margarine and speculaas spice. Mix with the dough hook of a hand mixer until large moist crumbs form, knead with hands to form a smooth dough.
Chop walnuts and mix with cane sugar. Form two rolls of the dough about 3-4 cm ø and roll them in the chopped walnuts. Wrap the rolls tightly with plastic wrap and rest in the refrigerator for 1 hour. Cut the rolls into 1/2 cm thick pieces, place them on baking trays lined with parchment paper and bake in a heated convection oven at 160 °C for about 15 minutes.