Potato, Mushroom, and Leek Croquettes

Ingredients

• 0.5 teaspoon pepper black freshly ground
• 4 ounces button mushrooms sliced
• 4 ounces cremini mushrooms sliced
• 1 large egg white 
• 1 large egg yolk 
• 0.3 cup flour all-purpose
• 1 teaspoon thyme leaves fresh chopped
• 2 ounces gruyère cheese shredded
• 0.5 teaspoon kosher salt 
• 0.5 cup leek chopped
• 1 tablespoon olive oil 
• 0.5 cup panko bread crumbs (Japanese breadcrumbs)
• 1 ounce parmigiano-reggiano cheese divided grated
• 2 teaspoons water 
• 8 ounces yukon gold potatoes peeled coarsely chopped

Equipment

• food processor
• bowl
• frying pan
• whisk
• potato ricer

Directions

1. Place potato in a pan; cover with water. Bring to a boil. Reduce heat; simmer 8 minutes or until tender.
2. Drain. Press potato through a ricer or food mill into a bowl.
3. Place mushrooms, leek, and thyme in a food processor; pulse until finely chopped.
4. Heat a large skillet over medium heat. Coat pan with cooking spray.
5. Add mushroom mixture; cook 6 minutes, stirring occasionally.
6. Add mixture to potato.
7. Add Gruyre, 2 tablespoons Parmigiano-Reggiano, salt, pepper, and egg yolk; stir until blended. Shape mixture into 8 (2-inch) round patties.
8. Place flour in a shallow dish.
9. Combine egg white and 2 teaspoons water in a shallow dish, stirring with a whisk.
10. Combine remaining 2 tablespoons Parmigiano-Reggiano and panko in a shallow dish. Dredge patties in flour. Dip in egg mixture; dredge in panko mixture.
11. Heat a large nonstick skillet over medium-high heat.
12. Add oil; swirl to coat.
13. Add patties; cook 4 minutes on each side or until golden.