How to Make It
Cut off both ends of the plantains and score them lengthwise, then peel off the skin. In a large bowl, combine the water with 1 teaspoon of salt. Add the plantains and let soak for 30 minutes. Drain and pat dry with paper towels. Cut each plantain on the diagonal into 6 slices about 1 1/2 inches thick.
In a large skillet, heat the oil to 275°. Add the plantain slices and fry, stirring, for 2 minutes. Transfer the plantain slices to paper towels and let cool slightly. Reserve the oil in the skillet.
Wrap each plantain slice in a dampened paper towel and use a meat pounder to gently pound it into a 1/4-inch-thick oval.
In a small bowl, using a spoon, stir to combine the sour cream with the chopped dill and lime juice.
Reheat the oil to 375°. Add the flattened plantain slices and fry, turning once, until golden and crisp, about 2 minutes. Drain the tostones on paper towels, then sprinkle with salt.
Dollop 1 1/2 teaspoons of the herbed sour cream on each tostone. Top with a slice of smoked salmon, garnish with a dill sprig and lime slice and serve.