• Prep the Onions or Shallots

  Peel and slice very thin, about 1/16 to 1/8 inch thick.

  Separate the slices into rings so they coat evenly and fry evenly.
• Optional Buttermilk Soak

  For a softer onion flavor and better flour adhesion, place the sliced onions or shallots in a bowl and cover with buttermilk.

  Let sit 15–30 minutes, then drain well.

  (Do not rinse. A light coating of buttermilk should remain.)
• Heat the Oil

  Add 1/2 to 1 inch of avocado oil or beef tallow to a heavy skillet or Dutch oven.

  Heat over medium-high until it reaches 350–365°F.

  If you don’t have a thermometer, test by dipping in a single slice — it should sizzle immediately without scorching.
• Mix the Seasoned Flour

  In a wide bowl, whisk together:

  Flour

  Cajun seasoning

  Salt

  Make sure the seasoning is evenly dispersed throughout the flour.
• Dredge

  Add a handful of drained onions or shallots to the seasoned flour.

  Toss to coat lightly.

  Shake off excess flour — too much coating will make them heavy, not crisp.

  Spread dredged pieces on a tray so they don’t clump.
• Fry in Small Batches

  Fry a loose layer of onion slices at a time — do not crowd the pan.

  Cook 1–2 minutes, stirring gently, until pale golden.

  They will darken slightly as they cool, so pull them just before deep brown.
• Drain and Season

  Transfer fried onions to a cooling rack set over a sheet pan, or a paper towel–lined tray.

  While still hot, sprinkle with a pinch of extra salt or Cajun seasoning to taste.

  Repeat with remaining onions, keeping the oil near 350°F and skimming out any loose crumbs between batches for a clean fry.

Make-Ahead & Recrisping

• Store loosely covered at room temperature for up to 48 hours.

  To re-crisp, bake at 300°F for 3–5 minutes.

  If topping a casserole, add during the last 5 minutes of baking, not from the beginning.