Blend first 4 ingredients in processor until nuts are coarsely chopped. Add butter; using on/off turns, blend until coarse crumbs form.
Preheat oven to 350 degrees F/180 degrees C. Butter and flour a 9 x 13 x 2-inch metal baking pan. Sift flour, baking powder, salt, and baking soda into medium bowl. Using electric mixer, beat butter in large bowl until fluffy. Gradually add both sugars and beat until well blended. Beat in eggs, 1 at a time, then lemon peel and vanilla. Blend sour cream and milk in small bowl. Beat in sour cream mixture alternately with dry ingredients in 3 additions each. Spread half of cake batter in prepared pan. Sprinkle half of topping over; cover with pears. Spread remaining batter over; sprinkle with remaining topping.
Bake until top is brown and tester inserted into center comes out clean, about 50 minutes. Cool cake completely in pan on rack. (Can be made 1 day ahead. Cover and store at room temperature.)
Makes 12 servings.
Source: Bon Appétit, October 2003
Date: January 31, 2007