Add the butter to a large pot set over medium heat. Stir in the onions, garlic, and celery then saute them just until softened and the onions are translucent.
2 tbsp butter, 2 cups diced yellow onion, 20 cloves garlic, 2 cups celery
Add the squash and zucchini to the pot and stir them to combine.
1 large yellow summer squash, 1 large zucchini
Add the seasonings to the pot, again stirring them in to evenly incorporate.
3 tsp dried oregano, 3 tsp dried basil, 1/2 tsp crushed red pepper flakes, 1/2 tsp salt, 1 tsp ground pepper
Add the tomatoes, sauce, and broth- again stirring until everything's evenly combined.
1 14.5 oz can diced tomatoes, 1 15 oz can tomato sauce, 4 - 4 1/2 cups chicken broth
Bring to a boil then reduce the heat to low and simmer, just until the squash is tender, roughly 10-15 minutes.
Serve warm with crusty bread and enjoy!