Preheat oven to 300 degrees F
Cook ingredients on the stove top until softened
Puree softened ingredients (immersion blender works great for this)
Pour the tomato sauce into a roasting pan (non-stick is best, with straight sides)
Roast at 300 until it thickens, stirring periodically
When your spatula leaves a clear path when sweeping the bottom of the pan, it has reduced sufficiently
Pour into ice cube trays, freeze, then vacuum seal the cubes