Chill the marzipan and grate it coarsely. Alternatively, warm it slightly and puree it.
Beat the eggs for a few minutes until very frothy. Gradually add the marzipan, making sure the batter remains fluffy.
Pour the batter into the springform pan and bake for 15 minutes at 325°F. Reduce the heat to 250°F and bake for another 30 minutes. If it browns too quickly, cover it with aluminum foil. Be sure to test the center with a toothpick. If it comes out clean, the cake is done.