Cook the pasta (and save the pasta water!): Bring a large pot of heavily salted water to a boil. Add the pasta and cook until al dente. Set the timer for a few minutes less than the package instructions and then taste: the pasta should be just done, still with some firmness. The pasta should also taste salty from the salted water. Save out 1/2 cup pasta water using a glass measuring cup for the sauce, then quickly drain the pasta.
Make the garlic butter sauce: Mince the garlic. In a large skillet, heat the olive oil and butter over medium low heat. Add the garlic and red pepper flakes and cook 2 to 3 minutes until fragrant and garlic just starts to turn golden. Remove from the heat before garlic browns (watch it carefully because it can brown quickly!).
Serve: Toss with the drained pasta, grated Parmesan cheese, 1/4 teaspoon kosher salt, and just enough pasta water until saucy (we used 2 to 3 tablespoons pasta water). Taste again and add a few more pinches of salt if desired. Enjoy warm.
Notes
*Double this amount for a larger, more filling plate of pasta. You can also add sautéed veggies to the pasta (like mushrooms or kale), or complete your meal with a filling vegetable side dish or salad.