Bring a large pot of generously salted water to a rolling boil. Add the pasta and cook according to package directions until al dente. Before draining, reserve 1 cup of the starchy pasta water. Drain the pasta and set aside.

While the pasta is cooking, heat the olive oil in a large skillet or Dutch oven over medium heat. Add the minced garlic and red pepper flakes (if using) and cook for 1 minute until fragrant, being careful not to let the garlic brown.

Add the roughly chopped kale to the skillet. Cook, tossing frequently with tongs, until the kale has significantly wilted, which should take about 3-5 minutes. If the pan appears dry, add a splash of the reserved pasta water to help it wilt.

Pour in the vegetable broth (or reserved pasta water if you didn't use broth) and bring to a gentle simmer. Stir in the heavy cream and 1/4 cup of grated Parmesan cheese. Continue to cook for 2-3 minutes, stirring constantly, until the sauce slightly thickens.

Add the drained pasta to the skillet with the creamy kale sauce. Toss vigorously to ensure the pasta is evenly coated with the sauce. If the sauce appears too thick, add a tablespoon or two of the reserved pasta water at a time until you reach your desired consistency.

Stir in the fresh lemon juice. Season generously with salt and freshly ground black pepper to taste. Taste and adjust seasonings as needed.

Serve immediately in bowls, garnished with additional freshly grated Parmesan cheese and a sprinkle of red pepper flakes, if desired.