Gourmet Beef Burger with Mushrooms, Caramelized Onions & Green Pepper Sauce

Prepare caramelized onions: peel and thinly slice the onion. In a pan over medium heat, melt 10g of butter with 5g of olive oil. Add the onions and a pinch of salt. Cook for 8-10 minutes, stirring often, until soft and lightly golden. Set aside.

Sauté mushrooms: wipe and thinly slice the mushrooms. In the same pan over medium-high heat, melt 10g of butter. Arrange mushrooms in a single layer and let brown for 3 minutes without stirring. Stir, season with salt and pepper, cook for another 2-3 minutes. Set aside with onions.

Start green pepper sauce: in a saucepan, melt 15g of butter over medium heat. Add the chopped shallot and cook for 1-2 minutes without browning. Add green peppercorns and stir for 30 seconds.

Create creamy base: stir in mustard. Pour in beef broth and scrape up browned bits. Let reduce for 2 minutes.

Finish gourmet sauce: lower heat, pour in cream and simmer for 3-5 minutes until sauce coats the back of a spoon. Adjust salt and pepper.

Optional: off heat, add cognac, stir and return to very low heat for 30 seconds. Set sauce aside.

Toast buns: cut buns in half and toast the inside in a pan or oven for 1-2 minutes. Set aside.

Cook steaks: heat a very hot pan, lightly oil. Place steaks, season with salt and pepper. Cook 2-3 minutes per side for rare, 3-4 minutes for medium. At the end, lower heat and spoon 1-2 tablespoons of sauce over each steak for 30 seconds. Let rest 2 minutes.

Prepare green crunch: rinse and spin dry baby spinach leaves.

Assemble burgers: on bottom bun, place the steak, spoon sauce, add mushrooms, onions, spinach. Top with bun, press lightly and serve immediately.