Bring a large pot of water to a full boil. When the water boils, add a tablespoon of salt. Then add the pasta and cook just until al dente -- 9 minutes for linguine.
While the pasta is cooking, place a large skillet over medium-low heat. Add the butter and oil to the skillet. When the butter melts, add the mushrooms and a sprinkling of salt and pepper. Saute until the mushrooms are brown and most of their liquid has escaped -- about 5 minutes. Add the garlic and saute for just 30-60 seconds.
Add the kale to the skillet, plus 1/2 cup of the pasta water. Then cover the skillet, and let the kale steam until it barely wilts -- about 1 minute. Then stir in the lemon juice, red pepper flakes, and 1/2 cup of the Parmesan cheese.
Drain the pasta, and add to the skillet mixture. Add the remaining 1/2 cup of Parmesan, and stir gently to combine. Divide among 4 plates and enjoy!