Step 1In the bowl of a food processor or blender, combine the egg yolk, lemon juice, salt, mustard and chopped chiles, processing to combine. With the processor running, slowly drizzle in the oil to emulsify; if using a processer, scrape down the bowl once or twice to make sure all of the oil is incorporated and the ingredients are fully combined. This makes a generous cup of aioli. The aioli will keep, covered and refrigerated, for up to 1 week.
Step 1Clean and trim the spring onions, keeping about 3 inches of the green attached to each bulb. Keep the bulbs intact if small; halve or quarter the bulbs if large.
Step 2In a shallow baking dish or container large enough to hold the onions, whisk together the flour, cornmeal, onion powder, garlic powder and salt. In a separate shallow container, pour the buttermilk.
Step 3Dip the spring onions in buttermilk, then toss in the cornmeal flour mixture to coat. Place the onions on a tray lined with parchment until ready to fry.
Step 4Heat a heavy pot half-filled with oil until a thermometer inserted reads 350 degrees. Fry the spring onions, a few at a time, until golden brown, 3 to 5 minutes. Remove the onions with a slotted spoon and place on a cooling rack to drain. Repeat with the remaining onions.
Step 5Serve the onions on individual serving plates, topped with a sprinkling of salt and chopped parsley and next to a dipping bowl of aioli.