Whisk all the ingredients in a medium saucepan over medium heat and bring the mixture to a boil, stirring occasionally. Bring temperature down to simmer and let the sauce reduce to 2 cups, stirring frequently.

The sauce will keep up to 2 weeks in the fridge but also freezes well.

If making to serve immediately, preheat oven to 250F. Place two cooling racks over two rimmed baking sheets.

Slice onion into 1/2" thick slices and separate into rings. Add the onion rings to 1 1/2 cups flour, toss to coat and let sit for 30 min.

When ready to fry them up, mix the remaining flour (1 1/2 cups) with the cornstarch, garlic powder, onion powder, cayenne, sugar, and salt, in a large bowl.

Whisk together the beer, sparkling water, and egg in another large bowl. Gradually whisk in the dry ingredients, add in the extra 1/2 cup of flour if needed.

In a large wok or deep fryer heat oil to 350F. Work in batches and don't crowd the onions. Take the onion rings and coat them in the batter and then drop them into the oil.

Cook the onion rings until golden brown, turning once as needed. Take the onion rings out and place them on the prepared cookie sheets.

If making ahead to freeze let cool at this point or place in the oven to keep warm while you finish making the rest.

*Freeze on the cookie sheets, once frozen place in bags, and then back into the freezer. Reheat at 350F. for 10-15 min. or until heated through and crisp.