Heat oil in a large skillet over medium-high heat. Add onion and sauté for 3 minutes or until slightly wilted. Season with ½ teaspoon of the salt and ¼ teaspoon of the cayenne pepper. Add catfish pieces and sauté for 2 to 3 minutes. Stir in garlic and green onions. Sauté for 1 minute. Remove from the heat and cool.
Mix eggs, milk, baking powder and remaining ½ teaspoon salt and ¼ teaspoon cayenne pepper. Add flour, ¼ cup at a time, beating well until the batter is smooth. Fold in catfish mixture.
Heat shortening in a deep fryer or a large, heavy saucepan to 360° F on a deep-frying thermometer. Drop heaping spoonfuls of batter into the hot oil, one at a time. When the beignets pop to the surface, roll them around with a slotted spoon to brown evenly. Drain on paper towels. Sprinkle beignets with Rustic Rub, and serve with Rémoulade Dipping Sauce.
Mix all ingredients in a small bowl until well blended. The rub mixture can be stored in an airtight container for up to 3 months. Makes about 1 cup.
Rémoulade Dipping Sauce:
Place all ingredients in a food processor, and process for 30 seconds. Use immediately, or refrigerate the sauce for several days in an airtight container.
Makes 2 cups.