Soak sun-dried tomatoes in boiling water for 30 minutes.

Drain the soaked tomatoes, reserving the liquid.

Chop the soaked tomatoes coarsely.

In a saucepan, cook onion and garlic in butter over moderately low heat until softened.

Add canned tomatoes with juice to the saucepan, stirring to break them up.

Add the chopped sun-dried tomatoes, salt, and pepper to the sauce.

Simmer the sauce, uncovered, stirring occasionally, for 30 minutes.

Puree the sauce through a food mill or coarse sieve.

Chill the sauce, covered, for up to 1 week if storing for later use.