Make the Batter: Whisk together the cornmeal, flour, baking powder, baking soda, salt and cayenne in a large bowl. Whisk in the buttermilk, eggs and onion until combined. Let the batter sit at room temperature for 10 minutes, or up to 1 hour.
Make the Dipping Sauce: In a small bowl, whisk together the sour cream, mayonnaise and Sriracha. Cover and refrigerate until ready to serve.
Fry the Hush Puppies: Heat the oil in a large Dutch oven or deep cast iron skillet over medium-high heat to 350 degrees. Drop half of batter into oil in heaping tablespoons (I used a small cookie scoop) and fry until deep golden brown, 2 to 3 minutes, turning hush puppies halfway through cooking.
Transfer to a wire rack set over a double layer of paper towels and repeat with the remaining batter. Serve immediately. The hushpuppies can be refrigerated in an airtight container for up to 3 days.
Oil: While peanut oil or vegetable oil is recommended, you can use other oils with a high smoke point - corn, soybean, safflower, canola, cottonseed, or sunflower.
Mix-Ins: If you want to stir in some extra flavor, you can toss in frozen or canned whole corn kernels, chopped jalapeno, chopped bacon, a little shredded cheese, etc.
To Bake: While I highly, highly encourage you to fry these for maximize flavor and texture, you can bake them in a mini muffin tin at 450 degrees for 7 to 10 minutes.
Make-Ahead: You can mix together the batter up to 1 hour before frying the hush puppies.
Storing: Leftover hush puppies should be stored in a paper towel-lined airtight container in the refrigerator for up to 3 days.
Freezing: Once made, cool completely, then place on a baking sheet in the freezer until solid, 1 to 2 hours. Transfer them to a paper towel-lined zip-to freezer bag and freeze for up to 3 months.
Reheating: Hush puppies are definitely best eaten soon after being made but can be reheated in a 400-degree oven for about 5 minutes. If using frozen, microwave for about 1 minute to thaw before reheating in the oven.