Preheat oven to 350°.
Melt 1 1/2 tablespoons butter in a 9-inch cast-iron skillet, and add 1/4 cup pear nectar, 1/3 cup brown sugar, and 1/4 teaspoon cinnamon, stirring until combined. Bring to a boil, and cook over medium heat 1 minute or until syrupy, stirring constantly. Arrange pear slices in a circular pattern over syrupy mixture.
Lightly spoon flour into a dry measuring cup, and level with a knife. Combine flour, baking powder, and next 4 ingredients in a medium bowl.
Place 1/4 cup butter, granulated sugar, and 1/3 cup brown sugar in a medium bowl; beat with a mixer at medium speed until well blended (about 3 minutes). Add egg and vanilla; beat well.
Combine 1/4 cup pear nectar and milk. Add flour mixture to butter mixture alternately with milk mixture, beginning and ending with flour mixture. Stir in dates.
Spoon batter over pears, spreading batter to edges. Bake at 350° for 28 to 30 minutes or until a wooden pick inserted in center comes out clean. Cool in pan 5 minutes. Loosen cake from sides of pan using a narrow metal spatula. Carefully invert onto a plate. Cut into wedges; serve warm. Top each serving with 1/4 cup ice cream, if desired.