Gather your equipment: a heavy-bottomed skillet or Dutch oven, stirring spoon, measuring cups, and a sharp knife.
Combine the flour and oil in the skillet and cook over medium-low heat, stirring constantly, until the mixture deepens to a rich, chocolate brown color—about 10-15 minutes. This forms a flavorful roux, so patience is key.
While the roux cools slightly, chop the onion, green bell pepper, and celery into small, uniform pieces. Set aside to add later.
Add the chopped vegetables to the hot roux and cook for 8-10 minutes, stirring often. They should soften, release a sweet aroma, and become glossy and fragrant.
Pour in the stock slowly while stirring to prevent lumps, then bring the mixture to a gentle simmer. Let it cook for 10 minutes, allowing the sauce to thicken and deepen in color.
Add the fire-roasted diced tomatoes, paprika, cayenne, and thyme to the sauce. Stir well, then simmer for another 10 minutes until the sauce is rich and glossy.
Stir in the peeled, deveined shrimp, making sure they are coated in the sauce. Cook for 5-7 minutes until they turn pink, firm, and opaque, with a slight bounce when pressed.
Squeeze in the fresh lemon juice and stir. Taste the sauce and adjust salt, spice, or acidity as needed. Let it rest off the heat for 5 minutes to allow flavors to meld.
Serve the shrimp étouffée hot over fluffy white rice, garnished with chopped green onions or parsley if desired. Enjoy the comforting, smoky flavor and tender shrimp coated in thick, glossy sauce.