Add dairy free butter (or ghee) in a large deep skillet over MEDIUM heat. When butter is fully melted and a little bubbly, add diced onion, red bell pepper, and 2 pinches of salt. Sauté stirring occasionally until very soft, about 3-5 minutes.
Add spice blend: nutritional yeast, salt, chili powder, cumin, paprika, garlic powder, onion powder, turmeric, black pepper, celery seed, and minced garlic. Sauté stirring frequently until fragrant, about 30 seconds.
Sprinkle evenly with cassava flour and sauté stirring constantly until flour is incorporated and a thick paste is formed.
Add ½ cup vegetable broth a little at a time while whisking constantly to keep the mixture smooth. When broth is fully incorporated and a thinner paste is formed, add the remaining vegetable broth slowly. Continue whisking constantly until mixture is smooth.
Add tomato sauce and water. Mix until fully incorporated.
Bring to a boil and reduce heat to MEDIUM-LOW. Simmer uncovered until reduced by about ⅓. Remove from heat.
For a smoother sauce, allow to cool to room temperature and add to a blender. Blend until fully smooth. **
Use immediately in your favorite recipes or store in the refrigerator in an airtight container up to 7 days.