In a medium mixing bowl, whisk together the flour, yellow cornmeal, baking powder, sugar, baking soda, salt, and onion powder. Set aside.
In a small mixing bowl, whisk together the buttermilk and eggs until evenly combined. Pour this mixture into the dry ingredients and fold with a rubber spatula until just combined. (Do not overmix the batter.)
Cover and refrigerate for a minimum of 1 hour (up to 24 hours).
When you're ready to cook, preheat the oven to the “warm” setting (about 200 degrees F).
Pour 2 inches of canola oil into a high-sided Dutch oven or other heavy-bottom pot. Heat over medium-high heat until the oil reaches 350 degrees F.
Carefully drop 1 tablespoon of batter into the hot oil. Continue dropping in the batter, working in batches, being mindful not to overcrowd the pot. Fry for 3-4 minutes until the outsides are a crispy, golden brown.
Use a slotted spoon to remove the cooked hush puppies to a paper towel-lined plate to drain. Transfer to a baking sheet placed in the warm oven to keep the cooked hush puppies warm until all the batter is fried.
Transfer the hush puppies to a serving platter and serve with lemon wedges and tartar sauce for dipping, if desired.
Notes
If you don't have buttermilk on hand, you can make sour milk instead. Stir together 1 cup + 3 tablespoons of milk with 4 teaspoons of white vinegar. Let that sit for 5 minutes and then prepare the recipe as directed.