Preheat oven to 350°. In a large bowl, cream butter and sugars until light and fluffy. Beat in egg and vanilla. In another bowl, whisk flour, baking soda, cinnamon, baking powder and salt; gradually beat into creamed mixture. Stir in oats and, if desired, raisins., Shape into fourteen 1-1/4-in. balls; place 2-1/2 in. apart on ungreased baking sheets. Bake until golden brown, 11-13 minutes. Cool on pans 3 minutes. Remove to wire racks to cool completely., To assemble ice cream sandwiches, place 1/3 cup ice cream on bottom of a cookie. Top with a second cookie, pressing gently to flatten ice cream; place on a baking sheet. Repeat with remaining cookies and ice cream. Freeze until firm., Remove ice cream sandwiches from the freezer. Working over a small bowl, drizzle chocolate topping over half of each sandwich, allowing excess to drip off., Place on a waxed paper-lined baking sheet; freeze until serving. Wrap individually in waxed paper for longer storage.