California Bartlett pear coffee Cake * 3 Cups Unbleached all-purpose flour * 1 1/2 Tsp baking powder * 1 1/2 Tsp baking soda * 1/4 Tsp salt * 3/4 Cup (1 1/2 Sticks) unsalted butter, Room Temperature * 1 1/3 Cups granulated sugar * 4 eggs * 2 Tsp vanilla extract * 1 1/4 Cups sour cream * 3 Medium Firm But Ripe California Bartlett pears, Cut Into Bite-Sized Chunks * 3/4 Cup light brown sugar * 1 Tsp ground ginger * 1 Cup Medium-Chopped walnuts Makes 8 Servings.