Ultimate Dirty Burger

Name: Ultimate Dirty Burger
Prep time: 25 min
Cook time: 1 h
Total time: 1 h
Yield: 4 portions
Ingredients: 40 g dried onions; 500 g beef mince; 30 g unsalted butter; 1 tsp fine sea salt; 140 g onions; 125 g pickled gherkins; 15 g olive oil; 50 g brown sugar; 50 g cider vinegar; 40 g pickled gherkin liquid; 20 g Worcestershire sauce; 10 g white mustard seeds; 2 pinches ground cayenne pepper; 2 pinches ground black pepper; 8 slices streaky bacon; 4 slices Cheddar cheese; 4 brioche burger buns; 4 tsp mustard; 4 Tbsp ketchup; 1 red onion