Brunost Burger with Lingonberry-Bacon Jam

Ingredients

• 4 Servings
• 2 tbsp neutral oil
• 1 large yellow onion, sliced into thin rings
• 1/4 tsp salt
• 150 g bacon lardons
• 1/2 small red onion, finely chopped
• 3 tbsp lingonberry jam
• 680 g good-quality ground beef
• Salt and pepper, to season
• 8-12 slices of TINE Gudbrandsdalen
• 4 burger buns
• 4 tbsp mayonnaise
• 2 handfuls of baby spinach leaves