I was trying to make royales for consomme for the first time, since I figured I already have spare yolks already. Following a recipe for custard in general that said one can use as much as 4 yolks per cup of custard to make it "firmer", I used the 7 yolks I had left with 1.5 cups of milk - more precisely, 125 g of yolk to 375 g of milk, and some salt, pepper, and chives.
I put this in a bowl over a pan of boiling water and whisked slowly, but the mixture never seemed to thicken significantly until it began curdling. (I tried to save this by immediately dumping the mixture into a pan and whisking out the curds as much as possible, which might be fine enough for slicing into soup, but I can't tell until this chills.)
Is there a method to follow to end up with firm, sliceable custard by double-boiling on the stove? I'd rather not have to fire up the oven for this. I also do have access to an instant-read thermometer, if stopping at a given temperature range will get me the proper result.