Place oil in a small cold nonstick frying pan and add garlic to the oil.
Tilt the pan so it is submerged in the oil and place over a medium heat. Use a wooden spoon to squeeze the garlic into the oil and gently fry until it's just starting to turn golden around the edges.

Now add the tomatoes, breaking them up with the spoon, then mash them with a potato masher.

Next add the salt & pepper, you can add more at the end to taste. Give sauce a stir and let it cook on medium heat, uncovered, stirring every minute or two until the sauce is the right consistency, about 10 minutes.

Now check the final seasoning. If it tastes bland, add a little more salt, stir and taste again. Be careful you don't add too much.

If it tastes bitter, add a little sugar. Cheaper tomatoes are usually bitter.

Finish by adding the basil.

If you over reduce the sauce, add a little pasta water to thin it out while serving. Pasta water is full of starch so it also helps emulsify, then you don't end up with a split sauce and have liquid under your spaghetti.