You can simply blend the tomatoes whole, just remove the core, and/or the seeds and skin. I Leave the seeds and skin. Blanch the fresh tomatoes in a pot of boiling water for 45 seconds to peel them easily. For frozen tomatoes, rinse them and the skins will come off easily. 

Scoop or squeeze out the seeds, then cut the tomatoes and process in a blender until smooth. This will make the tomatoes more pale in color, but it won't affect the flavor.

Put the oil into a sauté pan over medium high heat, then add the garlic (smash it under the flat blade of a large knife).

Then add the chopped parsley, but make sure it's dry or the water will make the oil squirt, so keep the lid handy, but don't keep the lid on.

When the garlic starts to brown, quickly add the tomatoes and cover with a lid to keep the squirting inside the pan, once it stops, remove the lid as quickly as possible. Stir with a wooden spoon, and keep it simmering quickly (don't lower the heat too much).

Add the salt.

This sauce cooks quickly, so you need to keep the lid off and stir often while it simmers/boils as there's a lot of water that needs to evaporate, especially if using frozen tomatoes.

When the sauce is thickened, after about 10 to 20 minutes, depending on the tomatoes used, taste and add salt if needed, then throw in some torn fresh basil leaves. Stir and turn off the heat.

Your sauce is now ready to use with pasta or whatever you want to use it for.