I am a meatloaf enthusiast. And I am devoted to hard boiled eggs. But I am not enthused about excessive onion. Could I cut this back to one onion and still have flavor? I would also be using what is called "meatloaf mix" here in New York. Equal parts beef/pork/veal for fat and flavor.
Nigella's version of Ed's Mother's Meatloaf (from KITCHEN) is moist and flavourful and some of this moisture comes from the onions that are slowly cooked in duck fat (or butter). It does seem quite a lot of onion, but as the onions cook they shrink in volume and should become very soft and slightly caramelized. So the meatloaf will not have the assertive, sharp flavour of raw onion but instead a mellow and sweet background flavour.
Our preference would be to keep the amount of onions stated in the recipe, but if you do feel that you have to reduce it then we would not reduce the onion by more than half (i.e. 250g/8 ounces) and keep the duck fat at 5 tablespoons. Meatloaf mix of ground beef, pork and veal is fine to use for the recipe, just make sure that the meat mixture is not too lean, particularly if the amount of onion is reduced, as the fat helps to keep the meatloaf moist.