Unfold pie shell; ease into 9-inch tart pan with removable bottom. Trim overhang to fit. Brush bottom with egg white.
Place baking sheet in oven. Heat oven to 400 degrees F.
Stir together sour cream, eggs, granulated sugar and vanilla in small bowl. Crumble together brown sugar, crumbs and butter in small bowl.
Peel, halve and core pears. Cut lengthwise into 1/4-inch-thick slices. Arrange slices in crust in 2 concentric rings, overlapping slightly.
Pour sour cream mixture over pears. Sprinkle with crumb topping.
Bake tart on heated baking sheet in 400 degree F oven for 40 minutes or until cream is set and top is lightly golden. Makes 8 servings.