Remove and discard all but 1 inch of the collard stems. Cut the remaining stems out of the leaves, separating the leaves and stems. Cut the leaves into 2-inch squares. Slice the stems into thin slices.
Wash the leaves in a big basin of water. Leave the water in the basin or sink and use a strainer to dip the leaves out of the water. Don't wash the leaves inside a colander or pour the water off the container with the leaves inside; this would allow any sand to stay with the greens. Wash the stems separately in the same basin of water, using the same method as the leaves.
Bring a large pot of water to a boil and add 2 tablespoons salt. Have a colander ready in the sink to drain the greens and a bowl of water with ice cubes in it to chill the greens.
Cook the stems for 1 minute. Add the leaves, and once they turn bright green, fish out a small leaf to taste it. The greens are done when they taste tender. You can't really tell whether the greens are done without tasting them.
Pour the cooked greens into the colander to drain. Once the hot water has drained off, carefully put the hot greens into the ice water. Once the greens feel cool to the touch, drain them in a colander again. Drain for about 10 to 15 minutes so that they are quite dry. (At this point, the greens may be stored in the refrigerator for up to 3 days.)
Put the olive oil in a large skillet over medium heat. Saute the onions gently in the oil. Raise the heat and add the peppers, and then the garlic. Add the blanched greens and saute until heated through. Season with salt and pepper.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.