For the salsa verde: Bring a large pot of water to a boil and add some salt. Add the tomatillos, garlic, cilantro, jalapeno and onion and bring back to a boil. Boil until the tomatillos turn olive green, about 10 minutes. Strain, reserving 1 cup of the cooking liquid. Transfer the ingredients from the pot to a blender with the reserved cooking liquid and puree until smooth. Return the mixture to the same (empty) pot, bring to a boil and boil until the sauce is darker green and reduced, 20 to 25 minutes. Season with 1 teaspoon salt or to taste and set aside.
For the enchiladas: Put the potatoes in a pot with enough water to cover, add some salt and cover the pot. Bring to a boil, lower to a simmer and simmer until the potatoes are fork-tender, 15 to 20 minutes. Drain and set aside.
Heat the olive oil in a large pan. Add the garlic and onion and saute until golden, about 5 minutes. Add the kale and saute until wilted, about 5 minutes more. Mix in the butter and 1/4 cup of the crema until melted and smooth. Gently mix in the potatoes and 1 cup of the cheese. Season to taste with salt and pepper. Set the filling aside.
Preheat the oven to 350 degrees F. Spray a 13-by-9-inch glass baking dish with nonstick cooking spray.
Heat enough vegetable oil to come 1 inch up the sides of a skillet to 350 degrees F over medium heat. Make an assembly line close to the stove top. Place half of the salsa verde in a cake pan (reserve the rest for topping) and put a cutting board and the potato-kale filling nearby.
Dip a tortilla in the hot oil until golden but still pliable. Using tongs, transfer it to the cake pan with the salsa verde and turn to coat. Place the dipped tortilla on the cutting board, stuff with a scant 1/4 cup of the potato-kale filling and roll up. Repeat with the remaining tortillas, salsa verde and filling.
Transfer the stuffed tortillas to the prepared baking dish. Top with the reserved salsa verde and remaining 1/4 cup crema and 1/4 cup cheese. Bake until darkened in spots, about 30 minutes. Serve slightly cooled.
Here's what's important in this recipe: dip the tortillas in hot oil first before dipping them in the salsa verde. This will ensure that they hold their shape. It can get messy. You are, after all, filling a salsa-drenched tortilla with filling, but it's so worth it. I like to keep a bowl with water and a rag so I can clean my fingers during the process and keep my hands clean.