Heat oven to 375°F. Prepare piecrust.
Combine brown sugar, flour, cinnamon, salt and cloves in bowl. Rub in butter with fingertips until crumbly. Stir in nuts.
In a large bowl, toss together apples and pears. In a medium-size bowl, stir together sugar, sour cream, flour and cinnamon and fold into apple-pear mixture.
Spoon filling into pie shell; tilt slightly so liquid flows evenly to all parts of pie shell. Top pie with crumb topping, mounding slightly. Place on small foil-lined baking sheet.
Bake in 375°F oven for 30 minutes. Reduce temperature to 350°F; bake 30 to 40 minutes more, until fruit is tender. If topping browns too quickly, loosely tent pie with aluminum foil. Let cool for at least 4 hours. (Can be made a day ahead. Cover pie and refrigerate.)
