What is the point of mustard-frying burger patties?
I did various tries and ate a lot of smashed cheeseburgers lately. Here is what I found:
The best option is, in the case of smashed burgers, to fry the first side without mustard, and the second side very briefly with mustard. This tastes better than frying without mustard at all, frying both sides with mustard, frying just the first side with mustard, smeering mustard on the patty after frying or adding more mustard into the sauce or elsewhere on the burger.
I cannot say why, but I can say that at least for my palate and my wife's palate mustard frying only the second side very briefly is best.