Several recipes in the Kuenstlichs und Fuertrefflichs Kochbuch specify clarified sugar. This entry tells us how to do that:
59 To Clarify Sugar
Take a seydlein (about 0.7 l) of water and the whites of two eggs to a pound of sugar. Beat it well so it foams and pour in the water, then beat that well together. Put in the sugar, let it boil gently (gemach sieden) and skim it well. Thus it is clarified. Let it boil well so it becomes somewhat thick (dicklet).
This is interesting because it provides fairly exact quantities. It is also short, which helps because I am very tired today. The result, I suspect, will be used as a heavy syrup rather than dry sugar, though it could of course be cooked down and dried out again. That also explains how clarified sugar and honey are used interchangeably as we will see in several recipes, and why a mixture of sugar and dry ingredients can be kneaded and moulded.
The short Kuenstlichs und Fuertrefflichs Kochbuch was first printed in Augsburg in 1559 and reprinted in Nuremberg in 1560 and subsequently. Despite its brevity, it is interesting especially as it contains many recipes for küchlein, baked or deep-fried confections, that apparently played a significant role in displaying status. We do not know who the famous cook referenced in the title may have been or if he ever existed.