In a large stock pot on medium-high heat, sauté onion with 2 tablespoons vegetable broth and garlic 3-5 min or until onion is translucent. Add 3 cups broth (save remaining 1 cup broth for later), water, lentils, saffron, coriander, cumin, black pepper, salt, and red pepper flakes. Reduce heat to low-medium and bring to simmer. Cover and cook until the lentils are no longer firm (15-18 min).
Very carefully pour the lentil mixture into a food processor (or blender) and puree until smooth. Depending on how big your food processor/blender is, you may need to do this in batches.
Put mixture back into the large stock pot and add remaining 1 cup broth and bay leaves; stir. Cook over low heat, uncovered, for about 10 minutes, stirring occasionally.
Remove bay leaves, add lemon juice and stir.
Once it sits for a few hours, it will soak up most of the liquid and thicken up a lot.