Heat the olive oil in a cast iron or heavy-bottomed pot over medium to low heat.
Add the chopped garlic and chilli flakes to the olive oil and cook until fragrant, about two to three minutes. If the garlic starts to brown, reduce the heat slightly. You just want to infuse the olive oil with garlic flavor.
Pour the crushed tomatoes into the pot. Give the sauce a good stir. Place the lid on the pot and leave it slightly ajar to allow steam to escape, and bring the sauce to a simmer for 10 minutes. Serve immediately, or let the pot sit on the stovetop, with the lid slightly ajar, for 4 hours to develop a deeper richer flavor.
Notes
Use a pot with a heavy bottom, like cast iron or enamelled cast iron, to prevent hot spots and help the sauce cook evenly.
Chop the garlic fairly evenly so it cooks at the same rate—small pieces are fine, but avoid mincing too finely, or it may burn quickly.
When you pour in the crushed tomatoes, do it carefully—they may splatter slightly when they hit the hot oil.
Keep the lid slightly ajar to let steam escape while simmering—this helps the sauce reduce and thicken.
Storage
Let the sauce cool completely before storing. You can keep it in a sealed container in the fridge for up to 5 days. It also freezes well. To reheat, warm gently on the stovetop or microwave, stirring occasionally until heated.