4 large ripe pears, peeled and chopped (about 4 cups)
3/4 cup all-purpose flour
3/4 cup old-fashioned oats
1/2 cup packed brown sugar
2 tablespoons chopped pecans
1/2 teaspoon ground cardamom
1/2 cup cold butter
On a lightly floured surface, roll dough to a 1/8-in.-thick circle; transfer to a 9-in. pie plate. Trim to 1/2 in. beyond rim of plate; flute edge. Refrigerate 30 minutes. Preheat oven to 400°.
In a small bowl, whisk egg, sour cream, sugar, flour, yogurt, vanilla and salt. Gently stir in pears. Pour into crust. Bake 15 minutes.
Meanwhile, for topping, in a small bowl, combine flour, oats, brown sugar, pecans and cardamom. Cut in butter until crumbly; sprinkle over pie.
Bake until a knife inserted in the center comes out clean and topping is golden brown, 15-20 minutes. Cover edge loosely with foil during the last 15 minutes if needed to prevent overbrowning. Remove foil. Cool completely on a wire rack. Store in the refrigerator.
Dough for single-crust pie: Combine 1-1/4 cups all-purpose flour and 1/4 tsp. salt; cut in 1/2 cup cold butter until crumbly. Gradually add 3-5 Tbsp. ice water, tossing with a fork until dough holds together when pressed. Shape into a disk; wrap and refrigerate 1 hour.