Heat olive oil and garlic in a deep saucepan over medium-low heat, stirring occasionally, until garlic is deep golden brown and fragrant, about 10 minutes.
Meanwhile, pour tomatoes into a large bowl and pull the firmer stem end from each tomato and discard along with any basil leaves that may be packed into the can. Crush tomatoes using your hands; set aside.
Add pepper flakes to saucepan and cook for 30 seconds. Add tomatoes and salt; stir to combine. Increase heat to medium and gently simmer, stirring occasionally, until thickened and reduced by a little more than half, about 2 hours.
Season sauce with salt and remove from heat; let cool.
Freeze for up to 3 months.