Burger Blue with mustard sauce and roasted onions

4 servings
  • 4 slices of Castello Burger Blue
  • 4 burger buns
  • 450 g ground beef
  • Salt and ground pepper
  • 2 red onions, in thick slices
  • 4 green lettuce leaves
  • 2 tomatoes, sliced
  • 4 whole pickles

Mustard sauce:

  • 250 ml sweet mustard, such as French’s
  • 4 tbsp acacia honey
  • 50 ml apple cider vinegar
  • 2 tbsp red chili, finely chopped
  • 2 tbsp ketchup
  • 2 tsp Worcestershire sauce
  • ½ tbsp garlic powder
  • Ground black pepper
  • Fries or potato wedges
  • Fresh thyme for sprinkling
Burger Blue with mustard sauce and roasted onions


Combine all the ingredients for the mustard sauce and refrigerate for a few of hours – preferably overnight.

Roast the onion slices until blackened on a very hot and dry pan. Divide them into onion rings and set aside.

Form the meat into 4 patties and season with salt and pepper.

Heat a grill pan until it is smoking hot. Fry the patties for about 3 minutes on each side – set them aside to rest.

Split the buns and warm or toast them. Place the cheese on the patties and spread the buns with mustard sauce, then top the buns with lettuce, patties, roasted onions and tomatoes. Finish with the top bun and serve with pickles, fries with a sprinkle of thyme and extra mustard sauce. 

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