3 green garlic, whites (chopped and lightly sauteed being careful not to burn) olive oil, divided
unsalted butter, divided
kosher salt to taste
3 large leeks, white and light green part only, cleaned and cut into 1/2-inch slices OR 1 yellow onion
3 lbs potatoes (or use 2 cauliflower heads and 4 turnips, peeled and cut into eighths, oven roasted)
1 medium head savoy cabbage
Place leeks (and turnips if using) in a roasting pan, dot with butter (approx. 1 tablespoon cut into pieces, or more, to your taste) and roast, covered, in a 350-degree oven until they are meltingly tender. Check periodically and lower the heat if they begin to burn. Loosen them from the bottom of the pan occasionally. May be made ahead of time. Let sit at room temp if making the entire dish on the same day, otherwise cover and chill. Peel potatoes and cut into 1 inch chunks and place in boiling water until tender. If using cauliflower, cut in florets and steam on the stove top, using a large pot and vegetable steamer, until they are very tender. Remove the florets from the steamer into a large colander and allow to drain. Heat a large pot of water to boil. Cut the savoy cabbage in half through the stem end. Using a sharp knife, remove the core from the end of each half. Cut the halves into quarters, or into pieces that will fit into the feed tube of your food processor. Using the slicing blade, process each section of cabbage until they are all sliced When the water in the pot is boiling, drop the sliced cabbage in all at once and blanch it for one minute, possibly longer, just to tenderize the cabbage. It's ready to remove from its water bath just when it turns a brighter green and is slightly softened.Drain the cabbage immediately through a large strainer set over a colander. Allow it to drain thoroughly. Using your food processor fitted with the regular blade, add the potatoes (or cauliflower and turnips), leeks (or onion) and garlic, and process until the mixture is smooth-ish, like whipped potatoes. You may have to do this in several batches, removing the processed mixture to a large bowl as I went along. Season the finished mash with kosher salt to taste. Fold in the cabbage and mix well. Mound into an ovenproof dish, dot with unsalted butter, and heat at 350-degrees for about 20 minutes, or until the mixture bubbles and the top is just golden brown.