Heat the olive oil in a large skillet over medium heat. Once hot, add the garlic and saute for 15-20 seconds until fragrant. Remove from the heat immediately and add the kale, red pepper flakes and the lemon zest from 1 lemon. Stir to combine. Let the kale wilt and set aside. Season with salt and pepper. Transfer the kale mixture to a food processor and add the optional pine nuts and pulse to combine for 45 seconds. Once it's semi-smooth, transfer it back to the skillet and set aside.
Cook the pasta according to the package directions and reserve ½ cup of the pasta water. Drain the pasta and reserve
Heat the kale mixture over medium heat to warm through. Add the pasta, parmesan, ricotta and a little bit of the reserved pasta water and stir to combine. If the sauce is too thick, add more pasta water to thin it out a bit. Taste and adjust salt, pepper, lemon zest, juice and red pepper flakes.