In a large pot, heat olive oil over medium low and add the onions, salt and pepper. Cook the onions until soft and caramelized, about 20-30 minutes, stirring occasionally. Add garlic and stir until fragrant, about 1 additional minute.
Add ½ cup of water and stir to deglaze. Stir in the remaining water and tomatoes.
Increase the heat to medium-high and bring to a simmer. Allow to cook for 20-30 minutes until the tomatoes are very soft.
Remove from heat and use an immersion blender to blend until smooth.
Serve hot.
Notes
LeftoversStore leftovers in an airtight container in the refrigerator for up to 4 days or freeze for up to 3 months. Reheat in the microwave or on the stove.