Warm up some whole milk. Important: Do not boil, because then it will no longer foam properly. Then froth up with a milk frother and let stand for 1-2 minutes so that the foam no longer collapses.
Then pour the foam and the warm, non-foamed milk into a glass. The amount of the non-foamed milk should be roughly the same as that of the espresso, rather a little more. Then pour in the espresso very slowly. If you do it too quickly, the espresso will mix with the milk, so be careful! I always use a spoon to help. The espresso can easily be poured in at the edge because nothing runs off and it goes so slowly. This then creates the typical white-brown-white pattern.