For the Linzer dough
Cream the butter and sugar with the paddle attachment, starting on low speed and increasing to medium speed, until smooth, about 5 minutes. Combine the vanilla and eggs and add them gradually, scraping down the bowl and blending until smooth after each addition. Sift together the flour, cinnamon, cake crumbs, and baking powder. Turn off the mixer and add the dry ingredients all at once, mixing on low speed until just blended. Do not over mix. Add the hazelnuts and mix until just blended. Turn out the dough onto a lightly floured work surface. Scale the dough as desired. Wrap tightly and refrigerate for at least 1 hour before rolling. The dough can be held, under refrigeration for 2-3 days or frozen for 1 month.