Fill a medium pot with 4 inches (10 cm) of oil and heat over medium heat to 350˚F (180˚C).
In a large bowl, whisk together the flour, cornmeal, sugar, baking powder, salt, and Jazzy spice blend.
Using your fingers or a pastry cutter, add the butter and work into the flour mixture until it resembles a coarse meal and the butter pieces are no larger than peas.
Make a well in the center of the flour mixture and add the egg and buttermilk. Working from the center outward, gradually mix into the dry ingredients until a smooth batter forms. Add the jalapeño and onion and mix gently just to incorporate. Be careful not to overmix.
Working in batches, use a 1-ounce (28 G) ice cream scoop or tablespoon to quickly but carefully scoop 8-10 balls of batter into the hot oil. Adjust the heat to maintain the oil temperature. Cook, turning the hush puppies frequently with a slotted spoon or spider, until golden brown and puffy, about 4 minutes. Transfer to a rack lined with paper towels to drain and repeat with the rest of the batter.