DIY Shake Shack ‘Shroom Burger Gelson's

Ingredients

• ½ cup yellow mustard
• ¼ cup mayonnaise
• ¼ cup ketchup
• 2 Tbsp rough chopped cornichon pickles
• Kosher salt, to taste
• Freshly ground Gelson’s black pepper, to taste
• 4 large portobello mushrooms, stem removed
• ¼ cup canola oil, plus more for deep frying
• 2 tsp kosher salt, divided, plus more to taste
• 1 tsp freshly ground Gelson’s black pepper, divided
• 1 ½ cups plus ¼ tsp Gelson’s organic all-purpose flour, divided
• 3 Gelson’s large eggs plus 1 egg yolk, divided
• 2 cups panko breadcrumbs
• 1 ½ cups shredded muenster cheese
• ½ cup shredded cheddar cheese
• ½ tsp Gelson’s organic onion powder
• ½ tsp Gelson’s garlic powder
• ⅛ tsp Gelson’s cayenne powder
• 2 Tbsp unsalted butter
• 4 potato hamburger buns
• Butter lettuce, for serving
• Sliced tomato, for serving
• French fries, for serving