Onion rings with salt and vinegar

Name: Onion rings with salt and vinegar
Prep time: 15 min
Cook time: 25 min
Total time: 40 min
Cuisine: Australian
Ingredients: 3 onions, cut into 1cm-thick rings; 250 ml buttermilk (1 cup); Vinegar salt; 60 ml white wine vinegar (¼ cup); 50 gm sea salt flakes; 1½ tsp white peppercorns, coarsely crushed in a mortar and pestle; Lemon-infused vinegar; 180 ml white wine vinegar; Thinly peeled rind of ½ lemon; Buttermilk batter; 150 gm plain flour (1 cup); 125 ml buttermilk (½ cup); 80 ml beer