Heat oil in a heavy saucepan or Dutch oven with tall sides to 350 degrees F. The oil should only come halfway up the sides of the pan, but should completely immerse the whole onion.
Peel the skin off the onion, leaving the root end intact. Cut a small slice off the top. Starting at the top of the onion make a cut down 1 side toward the root, stopping 1/2-inch from the bottom. Make additional cuts at 1/8-inch intervals until there are cuts across the entire top of the onion.
Rotate the onion so the cuts are horizontal to you. Continue to cut at 1/8-inch intervals, forming a checkerboard pattern across the entire top of the onion. To help the onion "bloom," gently spread the "petals."
Combine the dry ingredients in a shallow bowl or pan. Dust the onion with the flour mixture. Combine milk and beaten egg in a small, deep bowl. Dip the dusted onion into the egg mixture and then back into the flour mixture.
When the oil has reached 350 degrees F, carefully submerge the onion in the oil and fry for 10 minutes, turning as needed, until a golden color. Remove and drain the excess oil.
Serve with a variety of sauces, such as a mild ranch dressing or a spicy barbecue sauce.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.
Recipe courtesy of Jeff Davies, The Mangy Moose, Jackson Hole, WY