1. Preheat the oven to 375ºF. Oil a 2-quart baking dish or gratin with olive oil. Bring a large pot of water to a boil while you stem and wash
the greens. Wash them in 2 changes of water, lifting them from the water so that the dirt stays behind. Fill a bowl with ice water.
2. When the water comes to a boil, add a tablespoon of salt, and the greens. Boil (blanch) the greens just until tender, 1 to 3 minutes,
depending on how sturdy your greens are. Beet greens and chard will be ready in a minute or two. Kale will take longer, about 3 minutes.
Using a slotted spoon or a skimmer, transfer the greens to the ice water. Let sit just until cool, a few minutes, then drain and squeeze out
excess water by taking up bunches of the greens, making a fist around them and squeezing. Chop coarsely and set aside.
3. Heat 1 tablespoon of the olive oil in a medium skillet (preferably nonstick) over medium heat and add the onion. Cook, stirring often,
until tender and just beginning to color, about 5 minutes. Add the garlic and cook for another 30 seconds to a minute, until fragrant, then
stir in the greens, the herbs, and 1/2 teaspoon salt. Stir together for a minute, just until the greens are well mixed with the onions and
coated with oil. Remove from the heat.
4. Beat the eggs in a medium-size bowl. Add 1/2 teaspoon salt, freshly ground pepper to taste, and the milk, and whisk together. Stir in
the rice, greens, and Gruyère. Scrape into the baking dish. Sprinkle the breadcrumbs over the top and drizzle on the remaining tablespoon
of oil. Place in the oven and bake 35 to 40 minutes, until the top is lightly browned. Serve hot or room temperature. This is also good cold
and makes a great lunch.
The blanched greens will keep in the refrigerator in a covered bowl for 3 or 4 days. The dish can be prepared through Step 3 up to a day
before assembling the gratin. Keep the cooked greens etc. in a covered bowl in the refrigerator. The gratin can be made a day ahead and
reheated. Leftovers will be good for 5 days.