Preheat oven to 375°.
Place first 3 ingredients in a large bowl; beat with a mixer at medium speed until well blended (about 2 minutes). Add egg; beat 2 minutes or until pale. Place chocolate chips in a small microwave-safe bowl, and microwave at high in 20-second intervals until completely melted, stirring after each interval. Add chocolate to sugar mixture; beat until combined. Stir in milk.
Lightly spoon flour into a dry measuring cup; level with a knife. Combine flour, unsweetened cocoa, and salt; add to sugar mixture, stirring just until batter is blended.
Scrape batter into an 8-inch square baking dish coated with cooking spray. Bake at 375° for 18 minutes or until completely set. Cool to room temperature in pan on a wire rack. Cut brownies into 9 equal portions.
Place one brownie portion on each of 9 small plates; top each brownie with 1/4 cup ice cream and about 1 1/2 tablespoons caramel syrup. Sprinkle chopped Cracker Jacks evenly over sundaes. Serve immediately.