Preheat the oven to 350°F (175°C). Pierce the potatoes with a fork and bake directly on the oven rack until very tender, about 1½ hours. Let cool slightly, then peel.
Grate the cooled peeled potatoes using the small holes of a box grater (or press through a ricer). Discard any overly dry outer bits if needed.
Spread the grated potato on a board to cool completely, then sprinkle with ½ teaspoon salt, drizzle 2 tablespoons olive oil, and sprinkle about ¾ of the flour over top.
Mix with a spatula, then gently knead by hand until a smooth, slightly tacky dough forms; add the remaining flour a little at a time only if sticky.
Line a baking sheet with parchment and lightly flour it. Divide the dough into 4 portions and roll each into a uniform 1-inch log on a lightly floured surface.
Cut logs into 2-inch pieces and roll each piece over the tines of a fork to make grooves. Place shaped gnocchi on the prepared baking 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 sliced garlic, and sizzle about 30 seconds until fragrant; transfer garlic and oil to a blender.
When the pot boils, 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.
Add nutritional yeast, miso, 2 teaspoons lemon juice, and a splash (about ⅓ cup) of the reserved kale cooking water to the blender; blend on high until completely smooth, adding more cooking water by tablespoons if needed. Season with salt and pepper to taste.
Return the pot of boiling water to a boil if needed, then cook the gnocchi in batches until they rise to the surface, about 1 minute. Use a slotted spoon to transfer cooked gnocchi directly into the bowl with the kale sauce.
Toss the gnocchi gently with the sauce, adding reserved cooking water a little at a time to loosen the sauce if necessary. Taste and adjust lemon, salt, or pepper as desired, then serve hot.