To make the soffritto, in a large sauté pan, warm the olive oil over medium-low heat. Stir in the onion and anchovies and sweat, stirring occasionally, for about 3 minutes, or until the onion has softened. Stir in the tomato paste and fry, stirring frequently, for about 7 minutes, or until the paste turns from bright red to a deep rust. You need to cook the tomato paste this long to develop the rich, full flavor of the soffritto. Deglaze the pan with the water, dislodging any browned bits from the pan bottom. Adjust the heat to low and simmer, partially covered, stirring every 10 minutes, for about 30 minutes, or until the mixture develops a pastelike texture. If the mixture starts to brown too quickly, stir in a splash of water and continue to simmer. Pass the soffritto through the medium or fine disk of a food mill into a bowl and set aside. Alternatively, smash the soffritto against the sides of the pan with the back of a wooden spoon. You should have about 3/4 cup. Set aside. Using kitchen shears or a sharp paring knife, remove the center ribs from the kale leaves. Cut the ribs crosswise into 1/2-inch-wide pieces and set aside. Stack 3 to 5 leaves, roll them up lengthwise, and cut crosswise to create 1-inch-wide ribbons. Repeat with the remaining leaves. Rinse the leaf pieces and rib pieces separately in several changes of water until the water is clear. Bring a large pot of salted water to a boil. Add the rib pieces and blanch for about 12 minutes, or until tender. Using a wire skimmer, transfer them to a large, towel-lined baking sheet to drain. Working in batches, add the leaves to the boiling water and blanch each batch for about 8 minutes, or until tender, then transfer to the baking sheet. Give the pot a quick rinse and return it to the stove. Add the olive oil and warm over medium heat. Stir in the soffritto and cook for about 1 minute, or until it is sizzling. Stir in the kale, add about 1/2 cup water, adjust the heat to low, and simmer the kale for about 5 minutes, or until it is very tender and has absorbed the flavor from the soffritto. If the kale is too dry, add a splash of water and continue braising. Taste for seasoning and add salt if needed. Transfer the kale to a warmed serving bowl and serve immediately.
