In a large bowl, whisk together flour, cornmeal, sugar, baking powder, salt, and cayenne. Add buttermilk, onion, egg, and chives and stir until just combined. (The dough will be thick and tacky.)

Using a small cookie scoop, form the mixture into small balls (about 2").

In a large deep skillet (or dutch oven), heat about 1" vegetable oil until oil is shimmering. (It should read about 375 ° on a candy thermometer.) Working in batches, carefully add hush puppies in a single layer using a large slotted spoon. Cook until deeply golden all over, 2 to 3 minutes per side. Immediately transfer cooked hush puppies to a paper towel-lined plate to drain excess oil. Sprinkle with more salt.

Serve hush puppies warm with tartar sauce.