In a medium saucepan, saute onions and garlic in the olive oil for a few minutes, until softened and fragrant.
Add the remaining ingredients and stir to combine.
Bring the sauce to a boil, then reduce to a simmer.
Continue lightly simmering the sauce for 15-20 minutes, or until it has thickened.
To make an extra thick sauce, simmer it longer, stirring regularly.
Cool before using on pizza.
