Grilled Burgers With Mushroom and Onion Jam | Saveur

Ingredients

• 6 tbsp. LAND O LAKES® European Style butter, divided
• 1 small onion, sliced 1/8-inch thick, about 1 3/4 cups
• Kosher salt
• 2 shiitake mushrooms, sliced 1/8-inch thick, about 1 cup
• 1 portabella mushroom, sliced 1/8-inch thick, about 2 cups
• 1 small shallot, minced
• 2 cups red wine
• ¹⁄₄ cup red wine vinegar
• 2 tbsp. heavy cream
• 1 tbsp. plus 1 tsp. brown sugar
• 4 tbsp. LAND O LAKES® European Style butter, softened
• 4 burger buns
• 1 ¹⁄₂ lb. ground beef (80% lean)
• 6 oz. Gruyere, cut into 1/8-inch slices
• ¹⁄₂ small head of radicchio, thinly sliced