Melt the butter in a large heavy saucepan or deep skillet over medium heat.
1 stick salted butter
Sprinkle in the flour and whisk continuously until the mixture is smooth.
½ cup all-purpose flour
Cook the roux, stirring or whisking often, until it turns light brown and smells toasted.
Add the celery, onion, and bell pepper to the roux and stir well to coat.
Cook the vegetables until softened, about 5 to 7 minutes.
Stir in the Cajun seasoning, seafood seasoning, and garlic.
1 teaspoon Slap Ya Mama Cajun seasoning, 2 teaspoons Old Bay seafood seasoning
Cook for about 30 seconds, just until the garlic is fragrant.
Gradually pour in the warm stock, stirring well after each addition so the sauce stays smooth.
Bring the mixture to a gentle simmer and cook until slightly thickened.