Fill a skillet about 1/3 way full of vegetable oil, and place on medium-high heat.
Slice the plantains on the diagonal, slicing into 1/2 inch slices.
When the oil is hot enough to sizzle, carefully add the slices to the oil, without overcrowding the skillet.
Brown the slices about 3 minutes on each side.
Remove slices from skillet with a slotted spoon and place on a paper-towel covered plate. (Note: the slices will NOT look cooked.)
With a mallet or a rolling pin, smash each slice.
Carefully, slide the slices back into the oil.
Fry the green plantains a second time, flipping once. This time, fry them until they are a nice golden brown, another 1-2 minutes per side.
Carefully remove them and place on fresh paper towels.
Sprinkle generously with sea salt or table salt.