How to Make It
In a large pot of boiling salted water, cook the pasta until al dente. Drain, reserving 1 cup of the cooking water.
Fill the pasta pot with 1 inch of water. Spread the cabbage in a steamer basket set over the pasta pot and top with the potato. Steam the vegetables until very tender, stirring once or twice, about 10 minutes. Pour off the water and wipe out the pot.
In the same pot, melt the butter in the olive oil. Add the garlic and cook over moderately high heat, stirring, until lightly browned, about 2 minutes. Add the cabbage and potato along with the rosemary and thyme and season with salt and pepper. Cook until slightly dry, about 2 minutes. Add the pasta with its cooking water and cook, stirring and breaking up the potato, until the sauce is creamy and thick, about 2 minutes. Remove from the heat and stir in the Fontina and the 1/4 cup of Parmigiano. Transfer the pasta to bowls and serve, passing extra grated cheese at the table.