Step 1In a steaming basket set over 1 inch of boiling water, steam the potatoes until tender, about 10 minutes. Set aside.
Step 2Meanwhile, bring a large pot of water to a boil, salt generously and add the kale. Blanch just until tender, about 2 to 3 minutes. Fill a bowl with cold water and strain the kale from the boiling water to the cold water, then drain, taking the kale up by the handful and squeezing out any excess water. Cut the blanched kale crosswise into strips and set aside.
Step 3Bring the water back to a boil and add the cabbage. Blanch 3 to 4 minutes, until tender. Strain into the bowl of cold water, then drain and squeeze out excess water. Set aside with the kale.
Step 4In a large, heavy skillet heated over medium-low heat, add 1 tablespoon butter and the oil. Add the leeks and sage and cook, stirring often, until the leeks begin to soften, about 3 minutes. Add a generous pinch of salt and continue to cook, stirring often, until the leeks are tender, an additional 3 to 5 minutes. Add the garlic and cook, stirring, until the garlic smells fragrant, about 1 minute. Add the remaining butter, the blanched kale, cabbage and steamed potatoes, and stir together over medium heat until the mixture is tender and fragrant, about 3 minutes. Season with salt and pepper to taste. Remove from the heat.
Step 5Bring the water back to a boil, add the pasta and cook to al dente. When the pasta is done, add 1/2 cup of the cooking water to the pan with the vegetables, then drain the pasta and add it to the pan or to a warm pasta bowl with the vegetables and the cheeses. Toss together and serve at once.