Meaty mushrooms and zesty mustard make this vegetarian-friendly dinner hearty and flavorful. The kale and beans add additional bulk and terrific texture.
Season a large pot of water with salt and bring to a boil. Put the oil in a large skillet over medium heat. When it's hot, add the mushrooms, sprinkle with salt and pepper, and raise the heat to medium-high. Cook, stirring occasionally, until they release their liquid and the pan begins to dry, 8-10 minutes.2.
Add the leek and garlic and sprinkle with salt and pepper. Cook, stirring often, until soft, 3-5 minutes. Add the kale and paprika, toss to coat, then pour in the wine and cook, scraping any browned bits off the bottom of the pan, until the wine has reduced by half, just a minute or 2.3.
Add the stock and the mustard and bring to a boil. Adjust the heat so the mixture bubbles gently, and cook, stirring occasionally, until the kale stems are soft and the leaves are silky, 10-15 minutes.4.
Meanwhile, add the pasta to the boiling water, and cook, stirring occasionally, for 5 minutes, then start tasting. When the pasta is tender but still has some bite, scoop out 1 cup of the cooking water, then drain.5.
Put the beans in a food processor with a spoonful or so of the cooking liquid from the pot; puree until smooth. When the kale is ready, stir in the beans. If the mixture is too thick, add more stock 1/4 cup at a time, stirring after each addition. Cook, stirring frequently, until the sauce is warmed through. Taste and adjust the seasoning, and serve hot, spooned over the pasta.