Onion rings with salt and vinegar

Ingredients

• 3 onions, cut into 1cm-thick rings
• 250 ml buttermilk (1 cup)
• For deep-frying: vegetable oil
• For dusting: seasoned plain flour
• 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