As the others have mentioned, it won't quite be the same ... however, it can be done, it just won't quite have the same flavor as there isn't a chance for the meat juices to transfer into the sauce, and some issues regarding mixing it back in with the cold pasta.
If I were going to try it, I'd brown the meat, remove some of the fat if it's a really fatty grind, then add some extra sauce (or even other liquid ... maybe dairy, for a classic bolognese) to let it simmer for a bit ... then toss the pasta in with it to reheat.
The extra sauce is the key, otherwise, the meat isn't going to blend in with sauce on the pasta, If you reheat the pasta in the fresh sauce, it should hopefully mix together more completely.
... but if I were to do it, and wanted to add a meat to an already cooked pasta, I'd probably not choose ground beef as a first choice; I'd probably cook up some sausages, cut it down to an appropriate size for the pasta you're dealing with, and mix that in, possibly adding some extra liquid when reheating the pasta.
Gerbil gave the basic reasons as to why this might be happening, but as for the 'how to recover' .... you have a few options:
- Wait for it to finish separating, and take the oil off, then serve without oil.
- If you still want some fat for mouthfeel, after separating, you can add some butter back into the warm (but not too hot) sauce, and stir 'til melted and combined.
- If going for a more gravy-like consistency, after separating, put the oil back into the pan, make a roux and follow the basic procedure for a béchamel, but use the juices in place of the milk.
- After separating, take some of the non-oil part, add an emulsifier (eg, mustard), then slowly whisk back in some fat, add some of the juices, then slowly add the rest of the fat 'til it's the consistency you want.
- Put it into a blender an mix (although, open the vent hole, then put a towel over the lid, and hold it down with one hand when you turn it on ... blending hot things can be a mess) or use a stick blender.
In the future, I would separate out the juice & fats before reducing. You never know quite how much fat will render out of a piece of meat, and I feel I can reduce the juices faster when there isn't fat in there, but I've never actually timed it. Or, you can go the roux / gravy route if you're in a hurry.
Best Answer
You can both chop or not chop the anchovies.
I do not: I just crush them in the pan, and thus do not have to clean up anchovy oil from my cutting board.
I usually use anchovies like that in combination with garlic or onion, so the heat is never high enough to burn anything. If your anchovies get burnt, lower the heat.