Cheesy Curry Veggie Turnovers

Name: Cheesy Curry Veggie Turnovers
Ingredients: 2 tablespoons unsalted butter; 3 medium cremini mushrooms, cut into 1/4-inch pieces; 1/2 cup diced leeks, white and light green parts (about 1/2 medium leek); Kosher salt; 1 tablespoon Madras curry powder; 1 cup 1-inch cauliflower florets; 1 plum tomato, cored and diced; 1/3 cup frozen peas, thawed; 1 sheet puff pastry, thawed according to package instructions; All-purpose flour, for dusting; 1 1/2 cups Sargento Fine Cut Shredded Sharp Cheddar (6 ounces); 1 large egg, beaten; Mango chutney, for serving, optional