How to Make It
In a medium saucepan, cover the potatoes with water and bring to a boil. Add a generous pinch of salt and simmer over moderate heat until the potatoes are just tender, about 12 minutes. Drain and return the potatoes to the saucepan to dry and cool completely. Using a box grater, coarsely grate the potatoes into a large bowl.
In a medium skillet, heat the olive oil until shimmering. Add the finely chopped scallions and the serranos and cook over moderate heat, stirring, until softened, about 3 minutes. Add the scallions and serranos to the potatoes and let cool.
Line a baking sheet with wax paper. Add the shrimp, egg, 2 tablespoons each of Cotija and chopped cilantro and 1 teaspoon of salt to the potatoes and fold gently to combine. Form the mixture into 6 patties, a scant 3/4 inch thick and transfer them to the baking sheet. Refrigerate the cakes until just chilled, about 20 minutes.
In a large, deep skillet, heat 1/2 inch of canola oil until shimmering. Add 3 of the shrimp cakes and fry over moderately high heat, turning once, until cooked through, about 5 minutes. Transfer the cakes to paper towels to drain. Repeat with the remaining 3 cakes.
Spoon the kale into shallow bowls and top with the shrimp cakes. Garnish with Cotija, chopped cilantro and the sliced scallions and serve right away.