Cut away the stems and thick ribs from the collard leaves and discard, then roll a stack of the leaves (five or six at a time) lengthwise and cut crosswise into 1/4-inch-wide strips, or narrower if desired.
Using the kitchen sink or a large pan, wash the greens using 3 or 4 changes of room-temperature water. Then place the washed and trimmed greens into a colander and drain well.
Meanwhile, heat 2 tablespoons oil in a large, heavy pot. Place about half of the greens at a time in the pot and sauté, stirring, for 5 or 6 minutes, or until the greens are wilted. Remove from pot.
Add 2 tablespoons oil and the remaining greens and sauté the same way and remove from pan. Add a little more oil to the pan if necessary. Stir in the onion, garlic, cinnamon or nutmeg and cook over low heat for 4 or 5 minutes or until the onions are tender and translucent.
Return the greens to the pot. Add the broth or water, salt and black pepper and mix well. Bring to a boil, reduce heat to middle-low, cover and cook the greens for about 20 minutes, turning them over several times, until the leaves are tender.
Meanwhile, heat 11/2 teaspoon oil in a small skillet. Stir in the sesame seeds, and heat over low heat, stirring, until just lightly brown, 3 or 4 minutes. Watch carefully and don't let the seeds burn. At serving, sprinkle the toasted seeds over the greens.