Preheat oven to 350 degrees F. Grease a 9-inch springform pan or 9x9x2-inch baking pan. Combine the 1 cup nuts, brown sugar, and cinnamon. For topping, cut the 1/4 cup butter into 1/3 cup flour to make coarse crumbs. Stir in 3/4 cup of the nut mixture. Set nut mixture and topping aside.

Toss pears with lemon juice; set aside. In a medium bowl combine the 1-3/4 cups flour, baking powder, soda, and salt; set aside. In a large bowl beat 1/2 cup butter with electric mixer 30 seconds. Beat in granulated sugar and vanilla. Add eggs, one at a time, beating well after each. Add flour mixture and sour cream alternately to batter. Beat on low speed after each addition until combined.

Spread two-thirds batter into the prepared pan. Sprinkle with reserved nut mixture. Layer pears over top. Gently spread remaining batter over pears. Sprinkle with reserved topping. Bake 10 minutes. For a chunky top, sprinkle with 1/2 cup more nuts. Bake 45 to 50 minutes more or until a wooden toothpick inserted in the center comes out clean. Cool in pan on a rack 10 minutes. Remove side of springform pan, if using. Cool at least 1 hour. Serve warm with whipped cream, if desired. Makes 12 servings.