Mini Onion Blossoms

Place an onion from 16 cipolline onions (about 1½ lb.), ends trimmed, peeled, root side down, on a cutting board and arrange chopsticks along 2 opposing sides. Using a long, thin knife, make 2 perpendicular cuts in onion, forming an X and stopping at chopsticks (you don’t want to cut all the way through). Rotate onion a quarter turn and make 2 more perpendicular cuts, cutting onion into eighths and stopping at chopsticks. Lay flat side of knife over onion and gently press down with the heel of your hand just to open up onion slightly (make sure it remains intact). Transfer to a rimmed baking sheet and repeat process with remaining onions.

Whisk together 1½ cups (188 g) all-purpose flour, 3 Tbsp. cornstarch, 1 Tbsp. chili powder, 1 Tbsp. Diamond Crystal or 1¾ tsp. Morton kosher salt, 1 Tbsp. garlic powder, and 1 Tbsp. smoked paprika in a medium bowl. Whisk 1¼ cups sour cream and ⅓ cup whole milk in a second medium bowl until smooth.

Pour vegetable oil into a medium Dutch oven or large heavy saucepan to come 3" up sides; fit with thermometer. Heat over medium until thermometer registers 350°.

While oil is heating up, working one at a time, gently open up onions further with your hands, separating some of the petals slightly but still making sure to keep onions intact. Dip onions in sour cream mixture, letting excess drip back into bowl, then dredge in flour mixture, sprinkling flour over top to coat thoroughly inside and out. Shake off excess and return to baking sheet.

Working in batches of 5 or so, carefully lower onions into oil with a spider or slotted spoon and fry, turning halfway through, until golden brown and very crisp, about 5 minutes. Transfer, root side up, to a wire rack set over paper towels; immediately sprinkle with salt.

Whisk together ¼ cup mayonnaise, 2 Tbsp. ketchup, 2 Tbsp. sour cream, 1 tsp. prepared horseradish, 1 tsp. Worcestershire sauce, and a pinch of cayenne pepper in a small bowl. Taste sauce and season with salt if needed (makes about ½ cup).

Arrange onions on a platter. Serve with sauce alongside for dipping. Do ahead: Sauce can be made 2 days ahead. Cover and chill.