On page 36 of Hanna Winsnes’ cook book:
You make this egg-punch from one pound of white sugar, one pot (about 1 litre) of Armagnac and one pot boiling water – according to taste of how strong you want the punch to be; but note that if you make it too strong the eggs will easily separate, which is also the case when you use rum instead of Armagnac.
12 to 14 egg yolks for this portion can be very good; if you want it richer, use 16. Beat them well while somebody else makes the punch (above), then pour them in slowly, so that the stream of eggs run like a thin cord; meanwhile beat the punch so it froths well and does not separate. It should be drunk warm. If you leave the punch over the fire in an enameled pot or a copper pan and beat the eggs in as it is boiling, it may look thick with four to five eggs less; but it will get a floury taste and doesn’t look as fine and frothy.
Read about Hanna Winsnes and the First Norwegian Cook Book.