Step 1: Bring a large pot of salted water to a boil and cook the pasta according to package directions until slightly under al dente. Reserve 1 cup of pasta water before draining.
Step 2: While pasta is cooking, melt 2 tablespoons of butter in a large skillet over medium heat. Add the breadcrumbs and a pinch of salt, stirring constantly until golden brown and crispy. Remove from the skillet and set aside.
Step 3: In the same skillet, melt the remaining 4 tablespoons of butter with the olive oil. Add the sliced garlic and red pepper flakes. Sauté for 2-3 minutes until the garlic is soft and aromatic but not browned.
Step 4: Add the drained pasta to the skillet along with 1/2 cup of the reserved pasta water. Toss vigorously over medium heat to coat the noodles.
Step 5: Stir in the Parmesan cheese and half of the toasted breadcrumbs. Add more pasta water if needed to create a smooth, buttery sauce.
Step 6: Remove from heat, stir in the fresh parsley, and season with salt and pepper. Serve immediately, topped with the remaining crunchy breadcrumbs.