01 -
Grab a small pan and pour in the olive oil. Smash the garlic cloves and add them with the basil and chili flakes. Heat on medium-low just until it gently bubbles. Let it rest for a couple of minutes before turning it off.
02 -
Cook the spaghetti until it's slightly firm (check the package instructions). Scoop out ½ cup of the water before draining the rest.
03 -
Peel the onion and cut it across the middle. Heat up butter with a drizzle of oil in a bigger pot on medium-low. Drop the onion halves cut-side down and cook until golden and fragrant, about 8 minutes.
04 -
Pour the canned tomatoes into the pot and smash them with a wooden spoon. Start a low boil, sprinkle in salt, cover, and let it bubble slowly for about 8 minutes.
05 -
Mix the oil you infused into the tomato sauce and throw in the saved pasta water. Simmer uncovered for 5 more minutes. Scoop out the onion halves, then blend the sauce until smooth with a hand blender.
06 -
Stir the cooked spaghetti into the sauce so every bit is coated. Serve hot, tossing on some fresh basil or Parmesan if you'd like.