Potato and Blue Cheese Tart | America's Test Kitchen

Ingredients

• 1½ (7½ ounces/213 grams) (7½ ounces/213 grams) all-purpose flour
• 1 teaspoon table salt , divided
• 10 tablespoons unsalted butter , cut into ½-inch pieces and chilled
• 6-7 tablespoons ice water
• 4 ounces (113 grams) cream cheese
• 2 ounces (57 grams) blue cheese , crumbled (½ cup), divided
• 1 ounce (28 grams) Parmesan cheese , grated (½ cup), divided
• 2 tablespoons extra-virgin olive oil
• 2 teaspoons Dijon mustard
• 1 1/2 teaspoons minced fresh rosemary , divided
• 1/4 teaspoon pepper
• 1 large egg , separated
• 1 pound russet potatoes , peeled and sliced ⅛-inch thick
• 1 shallot , sliced thin