Crispy twice-fried plantains are a staple throughout many Latin American countries, including Puerto Rico, where my family is from. They're eaten at just about any time of day and in many ways—as a side dish along with entrees like pork or fish, as the base for savory party canapes or even as a salty late-night bar snack with a variety of dipping sauces. Here we serve them with garlic mojo (from the Spanish word "mojar" which means "to wet")—a tangy and spicy condiment made with fresh citrus juice, olive oil, garlic and herbs. Mojo is typically made with sour orange juice from Seville oranges, but as those aren't readily available you can use a mix of lime and regular orange juice to approximate the flavor.
For the mojo: Finely mince or use a rasp grater to grate the garlic into a small bowl or the base of a mortar and pestle. Add the salt and pepper and use a fork or the pestle to mash into a paste. Strip the oregano and cilantro leaves off the stems and add them to the bowl, mashing them into the paste. Whisk in the sour orange juice or equal parts lime and orange juice and the olive oil. Taste and add additional salt if desired. Set aside while you prepare the tostones.
For the tostones: Heat 3 inches of vegetable oil in a medium heavy-bottomed pot or Dutch oven until it reaches 325 degrees F on a deep-fry thermometer.
While the oil heats, peel the plantains and cut on the bias into 2-inch-thick pieces.
Fry the plantains in batches until crisp and pale yellow, about 2 minutes. Remove from the oil with a slotted spoon and drain on paper-towel-lined baking sheets. Repeat with the remaining plantains.
Move the pot the off the heat (do not discard the oil).
Line a cutting board with parchment paper and gather a flat-bottomed glass and small bowl of water. Place a fried plantain on the parchment paper, dip the bottom of the glass in the water and use it to smash the plantain to about 1/2-inch thick. Repeat with the rest of the plantains.
Put the oil on the heat again and bring it back up to 325 degrees F. Fry the smashed plantains in batches until golden and crisp, 1 to 2 minutes. Drain on paper towels, season with salt and serve hot with the garlic mojo dipping sauce.
If preferred, the sauce can be made by combining the ingredients in a food processor or blender and pulsing just until combined.