Preheat oven to 450ºF/230C and line a big baking tray with parchment paper.

Peel the onions without cutting them if possible.

Slice the onions lentghways into ¾ inch thick rings. Separate the rings and place them in a bowl.

Add the cornstarch and allpurpose flour in a deep bowl and mix.

Add about half of the dairy-free milk and stir vigorously with a whisk to a smooth batter. Add the rest of the dairy-free milk and the vinegar, and stir to incorporate.

Using a second bowl, mix together the bread crumbs and salt. Drizzle in the oil and use your fingertips to mix it up well.

Dip the onion rings first into the batter, making sure that you let the excess drip off, then drop them into the bowl with breadcrumbs, ensuring that they are coated all the way. Then add them to the parchment paper tray.

Make sure that you don't pile the onion rings on top of each other, or let them stick, they need distance from the others.

Bake the onion rings in the oven for about 8-10 minutes. Flip, and bake another 5 minutes.