In a medium Dutch-oven or heavy-bottomed pot, melt the butter with the stove on medium heat.
Add the flour to the butter and stir continuously (about 7 minutes) to make a dark brown roux.
Add the onions, garlic, green bell peppers, and celery to the roux and cook until softened (about 5 minutes).
Add the tomatoes, bay leaves, salt, cayenne pepper, and Cajun spice mix.
Add the shrimp stock.
Cover the pot and bring the stew to a boil with the stove on medium heat.
Turn the heat to low and let the stew simmer for about 30 minutes, stirring occasionally to prevent burning. You can add more shrimp stock if the stew gets too thick for your liking.
Turn the heat up to low-medium. Add the shrimp and cook for 5 minutes.
Add the parsley, cook for another 5 minutes.
Remove the bay leaves from the stew and serve the stew with steamed rice. Garnish with green onions, if desired.