Cut the ends off of each plantain, and use a knife to cut through the skin of the plantain, lengthwise, from top to bottom. Try to only to cut through the skin, as you don’t want to slice into the inner portion, which will form the Tostones.
Use your fingers to pry open and peel off the tough outer skin. Discard the skin of the plantains.
Cut the plantains into pieces, about 1″ thick.
Fill a large skillet about a third of the way with oil. Heat over medium-high for a few minutes to warm up the oil.
Take one plantain and carefully place it in the oil. If the oil surrounding the plantain begins to bubble a bit, the oil is hot enough.
When the oil is ready, add your plantains to the skillet. Fry them for about 2 minutes on each side, or just long enough to soften them and turn them a light golden color. Remove the fried plantains from the oil and place them on a paper towel to absorb some of the oil.
Using a tostonera, mallet, or the bottom of a cup flatten each fried plantain piece. I do this by placing one piece at a time on a cutting board and smashing it with the bottom of a cup. Smash them just enough that they flatten out, but don’t try to make them too thin, or they will break apart.
Return to now-smashed plantain pieces to the hot oil and fry again. Turn them occasionally, until both sides are a deep golden color.
Remove the Tostones from the pan of oil, and place them on a paper towel again to absorb some of the oil. Sprinkle generously with salt and serve.