Preheat the oven to 350°F (175°C). Pierce the potatoes several times with a fork and bake directly on the oven rack until tender, about 1½ hours. Let cool slightly, then peel.
Using a box grater (or potato ricer), grate the peeled potatoes on the small holes. Discard any very tough outer pieces if needed. Spread the grated potato on a board and let cool completely.
When cool, sprinkle ½ teaspoon salt over the potatoes, drizzle 2 tablespoons olive oil, then sprinkle about ¾ of the 2/3 cup flour over them. Combine with a spatula, then gently knead into a smooth, slightly tacky dough. Add the remaining flour only as needed; avoid overworking.
Line a baking sheet with parchment and dust with flour. Divide the dough into four portions. On a floured surface, roll each portion into a 1-inch-thick log. Cut logs into 2-inch pieces and roll each piece on a fork to make grooves. Place gnocchi on the prepared sheet and set aside.
Bring a large pot of water to a boil. Meanwhile, heat 2 tablespoons olive oil in a small sauté pan over medium, add the sliced garlic and sizzle about 30 seconds until fragrant. Transfer the garlic and oil to an upright blender.
When the pot is boiling, add the chopped kale and cook 2–3 minutes until stems are slightly tender. Use a slotted spoon to transfer the kale to the blender.
To the blender with garlic and kale add 1½ tablespoons nutritional yeast, 1 tablespoon light miso, 2 teaspoons lemon juice, salt and pepper to taste, and about 1/3 cup of the reserved kale cooking water. Blend on high until completely smooth, adding more cooking water tablespoon by tablespoon if needed. Taste and adjust seasoning.
Bring the kale cooking water back to a boil and cook the gnocchi in batches. They are done when they float to the surface, about 1 minute. Use a slotted spoon to transfer cooked gnocchi to the bowl with the kale sauce.
Toss the gnocchi gently with the kale sauce, adding reserved cooking water as needed to loosen the sauce. Serve hot and season with additional lemon, salt, pepper, red pepper flakes, or vegan parmesan if desired.
