In a large stock pot, gently sauté garlic and onions and anchovies in olive oil until the onions are soft and translucent.
Add tomatoes, salt, brown sugar and pepper. Stir to combine all ingredients and bring to a boil.
Allow to boil gently for 15-30 minutes.
Using an immersion blender, carefully blend the mixture until the sauce is uniform and no bits of tomato skin are visible.
Depending on the water content of your tomatoes, you may want to boil it down further for a more concentrated flavour. Add the lemon juice last. Taste the sauce and add more salt and/or brown sugar according to taste. Allow to fully cool before transferring to smaller containers for freezing.