Combine first 5 ingredients; stir in onion and, if desired, jalapeño.
Whisk together buttermilk and egg; add to flour mixture.
Pour oil to a depth of 3 inches in a Dutch oven; heat to 375°. Drop batter by level tablespoonfuls into oil; fry, in batches, 5 to 7 minutes or until golden. Drain on paper towels.
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