The recipes for marzipan confections in that book use pure almond paste, which is high-carb and filled with sugar. The other low-carb cookbook is a Swedish book, Bakglädje med LCHF by Annika Rogneby (yes, I love to collect cookbooks in different languages, well, no wonder, I’m a linguist…).
Preheat oven to 350 degrees. Butter a loaf pan and dust with flour. Tap out the excess flour. In a food processor, pulverize together the sugar and marzipan until the mixture is in fine pieces. Transfer the mixture to a large bowl. Add the butter and almond extract and mix until light and fluffy, about 1-2 minutes.
You can add almond extract for enhancing the flavor. However, if you can get bitter almond flavor (NOT bitter almonds or bitter almond oil), that would give even more authentic marzipan flavor. I’ve bought my bitter almond flavor from Germany, but I wouldn’t wonder if you can buy bitter almond flavor online or even from your local store.
My sugar-free, low-carb marzipan experiment was a great opportunity to explore more of this Zsweet sweetener. For the first experiment, I used just some 3.5 oz (100 g) of both almond flour and Zsweet, one egg white and a couple of drops bitter almond flavor. The texture was perfect, but the taste was far too sweet.