heat oven to 350 degrees. butter a spring 9 inch spring form cake pan and set aside.
sift the dry ingredients together in a bowl and set aside.
peel, core and chop into bite-sized chunks the pears. melt one tablespoon of the butter in a saucepan over medium high heat and add the pears. saute until they just start to release their moisture and add one tablespoon of the brown sugar. cook until the pears start to brown and remove from heat. set aside.
cream the butter and 1/2 cup of brown sugar together in a large mixing bowl. beat until light and fluffy. add the eggs, one at a time, and beat in the molasses, vanilla extract and orange zest. mix in half the dry ingredients and then 1/2 the sour cream. mix in the rest of the dry ingredients and the rest of the sour cream. fold in the pears.
pour the batter into the pan and bake for 50 minutes or until the center of the cake comes clean when you insert a cake tester.
while the cake is in the oven you can make the glaze. place the orange juice, ginger slices and sugar in a pan. heat until the sugar is dissolved and then simmer until the mixture starts to thicken, about five minutes. remove from heat and let stand. when the cake is out of the oven and cooled slightly, remove the pieces of ginger and spoon the glaze over the cake.