Place a pan or cooking skillet on the stove and add the butter, allowing it to melt on medium heat.
As the butter starts melting, add the garlic, onion, and green bell paper to make them soften. Cook until the aroma rises.
Rest for 3-5 minutes, and occasionally shake the ingredients in the skillet. This helps them to cook well and soften them well.
After 4-5 mins, add the chicken or shrimp stock and the flour and stir continuously because the lumps will form.
Add diced tomatoes, pasted tomato, diced celery stems, cayenne pepper, Cajun seasoning, salt and pepper to taste. Toss them into the mixture and leave them on low heat for 15-20 minutes. Check simultaneously the cooking sauce is not too thick and not too thin.
As etouffee sauce is cooking, ready the shrimps by peeling and deveining if needed. Lightly wash them under cold water and allow them to dry openly or with a paper towel.
After drying the shrimp, add them to the sauce and gently toss them until all their area is covered with sauce. Cover the skillet and allow it to cook for 5-7 mins because too much cooking makes them chewy and tough.
After the shrimp are cooked or turn to a pinkish-like color, Transfer them to a serving platter and sprinkle the sliced green onion over them to look presentable.