Many fried street snacks go into the oil twice, separated by a rest. The practice looks like extra work and is actually what allows a vendor to serve quickly without losing texture.
The first fry cooks the interior
At a moderate temperature, heat penetrates and cooks the inside through while the surface loses water gradually without hardening prematurely.
Going straight to high heat instead sets the outside before the middle is done, which produces the familiar failure of a dark shell around a raw center.
After this stage the item is cooked but pale and only lightly crisp, which is why it looks unfinished coming out.
The rest lets moisture redistribute
During the pause, water moves from the wetter interior toward the drier surface layer and evaporates from it.
That leaves the outer layer with less water to remove during the second fry, which is what allows the crust to form quickly and thoroughly.
The rest also lets the item cool, and cooling matters because starting the second fry from cold gives a longer window before the interior overcooks.
The second fry builds the crust
At a higher temperature, the prepared surface dehydrates rapidly and forms a rigid, porous layer that browns through the reactions between sugars and proteins.
Because that layer is thicker and drier than a single fry produces, it resists the moisture arriving from inside for far longer.
The practical consequence is a snack that is still crisp when it reaches a customer several minutes later, which is the whole point for a vendor.
Why this suits a stall's workflow
First frying can be done in batches during quiet periods and the results held, so the only work at the moment of ordering is a short second fry.
That collapses service time and lets one cook keep up with a queue, which single-stage frying makes impossible.
It also reduces waste, since a par-fried batch keeps for hours while a finished one has a life measured in minutes.
Doing it on an American stove
A heavy Dutch oven holds oil temperature better than a thin pot, which matters because adding cold food drops the temperature sharply.
A clip-on thermometer removes the guesswork, and frying in smaller batches keeps the oil from falling out of range between additions.
Neutral oils with high smoke points, including peanut, canola and refined sunflower, are all stocked by US supermarkets and all suit this method.