Put the olive oil and onion in a large pot and cook over medium heat, stirring frequently, until the onion begins to turn a light golden color, 5 to 7 minutes. Sprinkle in the sugar and cook, stirring continuously until the onion turns a deep caramel brown color, 5 to 7 minutes more.

While the onion cooks, prepare the kale leaves. Rinse each leaf thoroughly under cold running water; do not dry them. Snap off the tough parts of the stems and discard. Bunch together several leaves at a time and, with a sharp knife, cut carefully across the bunch at 1/2-inch intervals to make bite-sized strips. Set aside.

When the onion is browned, add the kale to the pot with the moisture still clinging to it. Stir with a wooden spoon to mix the onion with the kale and pack the kale down into the pot. Reduce the heat to low, cover securely, and cook until the kale is fairly tender, 30 to 45 minutes, stirring occasionally. The kale will reduce considerably in volume.

While the kale cooks, bring another large pot filled with water to a boil. About 10 minutes or so before the kale is done, add the pasta to the water and cook until al dente, following the manufacturer's suggested cooking time.

Stir hot pepper sauce into the kale mixture to taste. Season with salt and pepper. As soon as the pasta is done, drain it and toss with the sauce. Serve immediately, passing Parmesan for guests to add.