Heat the olive oil in a 12" oven-safe skillet and add the garlic; saute until the garlic begins to sizzle.
Stir in the sage, then add the baby greens or cabbage and season with salt and pepper.
Saute, stirring occasionally, for 2 to 3 minutes, or until the vegetables are softened.
Turn the heat as low as possible and cover the skillet.
Put the potatoes in a 3 quart pot, add a teaspoon of salt, and cool water to cover.
Bring to a boil, then reduce the heat and simmer about 5 minutes, or just until the potatoes are tender.
Scoop the potatoes out of the water with a small sieve and put them into the skillet with the cabbage, leaving the pot of water on the heat.
Add hot water to the pot, if necessary, and bring back to a boil.
Stir in the pasta and cook until it's al dente.
Meanwhile, place an oven shelf 8" below the broiler and preheat the broiler to high.
Drain the pasta, reserving 1/2 cup of the cooking water, and return the pasta to the pot.
Stir the melted butter into the pasta, then add the pasta to the skillet with the vegetables.
Add all the cheese, toss to combine; stir in some of the pasta water if the mixture seems too dry.
Place the skillet under the pre-heated broiler for 4 or 5 minutes until the cheese is melted.