Chef Richard Blais created this burger recipe with mushrooms in mind, and they're not only included in the seasoning, mayonnaise, and ketchup, but in the burger blend, as well.
Simmer the button mushrooms in the cream for 15 minutes. Purée the mixture in a blender until completely smooth. Add the mayonnaise and seasonings and combine thoroughly.
In a pot, boil the curry powder, soy sauce, shiitake stems, and water until it reduces to approximately ½ cup of liquid. Strain and add the ketchup, hoisin sauce, and orange juice. Stir until combined and smooth.
In a small bowl, combine the first 4 ingredients and set aside.
In a pan with high-quality butter, roast the mushroom blend until golden. Then sprinkle with salt, pepper, and a squeeze of lemon juice. Place on a paper towel and cool. In a grinder, grind the roasted mushrooms. Alternatively, use a food processor and grind until fine. Use paper towel to blot out any remaining moisture.
Gently fold the cooked mushroom grind and beef grind together. Form the meat mixture into eight ¾-inch-thick patties. Season the burgers with the spice blend and salt and pepper on both sides. Cook in a pan or on a hot grill for 3-4 minutes per side. If cooking in a pan, toss in a pat of butter and sprigs of rosemary and thyme. Baste the burger as it cooks.
Toast the brioche or burger buns in butter or olive oil. Spread the Mushroom Ketchup and Mushroom Mayo on the bottom bun. Next, add caramelized onions followed by burger patty topped with melted Gruyère cheese. Finish with bread-and-butter pickles and top bun.