Heat a medium saucepan over medium-low heat. Add the olive oil to the pan, allowing it to warm for 1 minute, then add the garlic and sauté it for 2 minutes, stirring constantly, until it’s golden brown and fragrant.
Add the crushed tomatoes, salt, pepper, sugar and crushed red pepper flakes (optional), stirring to combine. Simmer the sauce for 7 minutes, stirring occasionally, then season it with additional salt, pepper or sugar, to taste.
Note: The strongest flavor of the marinara sauce will depend on what variety of crushed tomatoes you use.