Place it in a large bowl or the bowl of a standing mixer, add one egg, and start whisking together with a stand mixer, or by hand with a large balloon whisk.
After the first egg has been combined well with the marzipan, continue adding the eggs one at a time, mixing completely between each addition.
Whisk for about 10-12 minutes on high until your batter is fluffy and thick. If using chocolate chunks, stir them in now.
Pour into a pan and bake for 30-40 minutes, or until a skewer comes out clean.
Cool in the pan, glaze or decorate with a dusting of confectioners sugar as desired, and serve.