Boil the pasta: Bring a large pot of well-salted water to a boil. Cook the pasta until just shy of al dente. Reserve about 1 1/4 cups of the starchy pasta water, then drain.

Start the sauce base: While the pasta cooks, warm the olive oil in a large skillet over medium heat. Add the sliced garlic and cook, stirring, until it’s fragrant and just turning golden at the edges, about 1–2 minutes. Don’t let it brown too much or it will taste bitter.

Add a little heat: Sprinkle in the red pepper flakes and toast them in the oil for 15–20 seconds to bloom their flavor.

Build the emulsion: Pour in 3/4 cup of the reserved pasta water. It will sputter, so be careful. Swirl or stir to combine with the oil, forming a thin, glossy base.

Toss the pasta: Add the drained pasta to the skillet. Toss for 1–2 minutes, letting the pasta absorb some of the liquid. If it looks dry, add more pasta water a splash at a time.

Finish with cheese: Reduce heat to low. Sprinkle in the grated Parmesan gradually, tossing constantly to help it melt and cling without clumping. If using, add the butter for a silkier texture. Adjust with more pasta water as needed to keep it saucy, not sticky.

Brighten it up: Grate in a little lemon zest and add a tiny squeeze of lemon juice if you like. Taste and season with salt and black pepper.

Garnish and serve: Top with chopped parsley and toasted breadcrumbs if using. Finish with an extra snowfall of Parmesan. Serve right away while it’s glossy and hot.