Ketchup and Mustard Burger

1. Prepare fennel ketchup: In mixing bowl, thoroughly coat fennel, tomatoes, onion and garlic with olive oil, salt and pepper. Place fennel mixture onto sheet pan and roast in oven at 400 F for 10 minutes or until vegetables are caramelized.
2. Meanwhile, in medium saucepan over low heat, melt brown sugar until caramel forms. When brown sugar has completely melted, add roasted fennel mixture into saucepan. Mix vegetables and caramel together taking care not to burn. When sugar and vegetables have been thoroughly incorporated, remove from heat. Using immersion blender, blend together sugar and vegetable mixture until smooth. Add apple cider vinegar, tomato paste, salt and pepper. When mixture is smooth, strain through china cap strainer into storage container. Allow to cool and set aside.
3. Prepare roasted mushrooms: Toss mushrooms with oil and place on 375 F flat top. Allow mushrooms to caramelize on both sides. Hold hot and set aside. 
4. For burger patties: In mixing bowl, thoroughly blend ground beef, minced mushrooms, salt and pepper. Form seasoned beef-mushroom mixture into a 6-ounce patty. On a seasoned broiler or grill, cook burger patty to desired doneness.
5. To assemble: In mixing bowl, toss together mustard greens, olive oil, salt and pepper; set aside. Spread 1 1/2 tablespoons fennel ketchup on top of warm toasted onion bun. Place mustard greens mixture on bottom bun; top with grilled burger patty and roasted king trumpet mushrooms. Cover with top of onion bun. Serve hot.

Photo courtesy of Meat & Livestock Australia