Cook the pasta according to the package directions or whatever f***ing method you invented and now swear by. When it’s all done, throw it in a large bowl with the spinach, toss, and set aside.
While the pasta cooks, bring a medium pot of water to a boil. Throw in a pinch of salt and the cauliflower and simmer all that until the cauliflower is tender, 5 to 7 minutes. Drain the cauliflower and toss into a blender.
Add the milk, garlic, lemon juice, olive oil, miso and 1/8 teaspoon salt to the blender and let that motherf***er run until the sauce is creamy. Taste and adjust as you see fit.
Pour the cauliflower purée into the pot you boiled the cauliflower in and set over low heat. Add the pasta and spinach and toss until everything is mixed and warm. Top with some parsley, salt and pepper to taste. Serve hot.