Slice the ends off the plantains, then slit the skin lengthwise just deep enough to almost touch the inner fruit. Remove the plantain peel. Slice each plantain into roughly 1 1/2-inch thick sections.
Add 1 1/2 cups of vegetable or canola oil into a large-size cast iron pan. Heat over high heat for roughly 60-90 seconds, then reduce to medium heat.
Add the plantains to the hot oil, standing up on their ends. Try not to crowd the pan. When you see the plantains begin to turn golden on the sides, flip them over. It doesn't take too long for this to happen, about 30-60 seconds.
Once the plantains have turned golden on both ends, remove them to a paper-towel lined plate to drain some of the oil. Smash them down using a sturdy cup, then lay them in the bowl of salt water. I like to smash a few, lay them in the water bath, then smash a few more and remove the other ones from the water and set them back on the plate before adding more to the water.
Add the plantains back into the oil and fry for roughly 30 seconds on each side. They'll get a little darker in color, but you don't want them to get too dark. Be very careful when you add the plantains back into the oil. Water and hot oil don't mix very well, so there will be some splattering.
Once you have fried the plantains on both sides, remove them from the oil onto a fresh paper towel lined plate to drain the oil. Sprinkle them with salt right after they have come out of the oil. Repeat this process until you have fried all of the plantain sections.
Enjoy hot! These are delicious just salted or dipped in a sauce such as garlic aioli.