Step 1
Preheat broiler. On a baking sheet, toss onion, carrots and olive oil. Broil until onion begins to caramelize, about 15 minutes.In a slow cooker, add onion and carrot mixture.
Step 2
Mix with the rest of the ingredients. Put lid on slow cooker and turn to low. Cook for 4 hours.
Step 3
Mix and turn on high. Cook for another 4 hours. Turn off slow cooker. Using a hand blender, puree the tomato sauce until no large chunks remain.If freezing, let cool completely and freeze in heavy duty plastic bags.