Add the chicken broth, half and half, salt, onion powder, garlic powder, black pepper, and cayenne pepper to a medium saucepan and bring the mixture to a boil over medium-high heat. Slowly pour the grits into the pan while stirring with a wooden spoon so lumps do not form.
Lower the heat to medium, cover the pot, and simmer the grits for 35-45 minutes, or until tender and creamy, stirring occasionally.
Meanwhile, rinse and pat the catfish fillets dry. Brush both sides of each piece of fish with melted butter and coat each side with blackened seasoning, rubbing it into the fish with your hands.
Heat 1 tablespoon of extra-virgin olive oil over medium-high heat in a 10-inch cast-iron skillet. Place the catfish in the heated skillet and cook for 3-5 minutes per side until a charred crust forms on the outside and it is cooked through. Transfer the fish to a paper towel-lined plate.
In the same skillet that you cooked the fish in, melt two tablespoons of butter over medium-high heat. Add the chopped onion and bell pepper and cook for 2 to 3 until the onion is translucent. Add the garlic and cook for another minute, stirring constantly with a wooden spoon.
Pour the chicken broth and heavy cream into the skillet and season with blackened seasoning. Cook the sauce for 4 to 6 minutes until it thickens and coats the back of a spoon. Remove the pan from the heat.