Almond Paste Filling

In the bowl of a 5-quart (5 L) stand mixer, soften the almond paste by mixing it at low speed with a paddle attachment. Add the lemon zest and mix it in. Slowly add the egg whites and mix until a soft consistency is achieved. You may not need to add all of the whites. The filling should be able to be rolled out into logs without having to add any flour to prevent sticking.