Mrs. Beeton again.

It really was a surprisingly acceptable substitute for milk, though different (less sweet, less white, more filling). Like soy milk substitution, I don't think I'll take up pouring beaten egg into my coffee regularly. 

Yeah, egg in coffee. I needed the conjunction of a fresh-laid egg and nerve. The egg has become easier, fowl houses are fashionable among my friends (and if any of you want to start with bantams I think I know 3 young hens in search of a good home) and so the nerve was provided by the example of my daughters keenly eating raw egg out of bowls this afternoon. For those concerned about the possibility of eggy lumps in the coffee: there were a few, they sank. I left that half inch in the bottom. 

I think I'm more likely to take up still more nutritrious coffee though I might try to do it without boiling either the milk or the coffee. 

NUTRITIOUS COFFEE.
1864. INGREDIENTS - 1/2 oz. of ground coffee, 1 pint of milk.

Mode.—Let the coffee be freshly ground; put it into a saucepan, with the milk, which should be made nearly boiling before the coffee is put in, and boil both together for 3 minutes; clear it by pouring some of it into a cup, and then back again, and leave it on the hob for a few minutes to settle thoroughly. This coffee may be made still more nutritious by the addition of an egg well beaten, and put into the coffee-cup.

Time.—5 minutes to boil, 5 minutes to settle.

Sufficient to make 1 large breakfast-cupful of coffee. 

(This recipe also from Mrs. Beeton's Book of Household Management, first published in 1859-61, now available from http://www.mrsbeeton.com/)

I'm reading Kathryn Hughes' biography of Isabella Beeton, a book better than eggy coffee.