Finely chop or puree the butter with the dates and the lemon zest in a food processor with a cleaver. Then add the egg and mash for a few more minutes. Now add the flour little by little (e.g. individual tablespoons full) and, in between, always stir or knead the mixture well with the machine. Put the dough in a freezer bag and press flat and smooth. Then let the dough rest in the refrigerator for at least 1 hour.
Roll out the cooled dough on a floured work surface to a thickness of approx. 3 mm and process as desired.
In the meantime, preheat the oven to 200 ° C top / bottom heat. Place the formed dough on baking sheets lined with baking paper and bake for about 10 minutes.