Preheat your steam oven to Steam, 212F/100C (100% humidity).
While the oven preheats, wash the kale well, and cut the ribs from the center of each leaf. You'll have to decide here if you think the ribs are tender enough to use - if they're very large and tough I save them to add to a soup or stock, as they'll give this dish a chunky texture that's unwelcome. If you're using them, finely chop the ribs, and put them into the largest stainless steel tray that'll fit into your steam oven. Add a couple of tablespoons of water to the tray, then pile the kale leaves on top. It's going to be a lot in the pan but it will collapse. If you have a compact steam oven you may want to use two separate pans to contain all the kale.
1.5 lb kale
Put the kale into your preheated oven and steam for 10-12 minutes. The chopped ribs and the leaves should be tender but not mushy; you may need to adjust your cooking time depending on how thick and tough your kale leaves are. Curly kale will take the longest; Tuscan/Lacinato in between, and the softer Red Russian will have the shortest steaming time.
While the kale is cooking, heat a fry pan over medium heat and add the olive oil and garlic. Cook until the garlic begins to sizzle, then reduce heat to low, and cook very gently until garlic is soft and begins to turn light golden, about 5 minutes. Remove from heat.
¼ cup olive oil, 4 cloves garlic
When the kale is cooked, transfer it directly into a blender or food processor, along with the liquid from the steaming tray. Add the garlic and its oil, and the salt and pepper. Blend into a fine, thick green purée. You may need to add a little more hot water to get the sauce to blend to a smooth consistency. Taste and adjust seasoning if necessary, then blend again. Set aside while you cook the pasta.
1/2 tsp fine salt, 3/4 tsp ground black pepper
Bring a large pot of water to the boil, salt well, and cook your pasta according to directions on the package. Ladle out about a cup of the water and reserve, then drain the pasta and return it to the dry pot.
1 lb dried pasta
Add the kale purée and parmesan cheese, and a splash of the reserved pasta water. Add a big squeeze of lemon juice, if using, then toss until all the pasta is well coated and bright green. Add more pasta water if needed so that the sauce is loose and almost creamy in texture. Serve immediately in warmed bowls, with the ricotta cheese generously dotted over the top of each serving.
2/3 cup coarsely grated parmesan cheese, 1 lemon, 1 cup ricotta cheese