For the homemade yogurt, first boil the whole milk briefly and let it cool down again a bit. Cool down so that it has a lukewarm temperature (tip: you should no longer scald!). Then add the sugar cubes and the natural yogurt and mix. Put a cloth over the bowl and let it stand for 4 hours.
Attention: Do not put a lid over it. The yogurt must be allowed to “de-steam”, otherwise it will become watery rather than stiff. After the 4 hours, put the homemade yogurt in the refrigerator for 24 hours, leaving the cloth on top (do not open).