For the crust: Cut the butter into pats and add to a medium heatproof bowl along with the chocolate chips. Place the bowl over 1 inch of simmering water, making sure the bowl doesn't touch the water. Once the butter and chocolate start to melt, stir to combine and remove from the heat. Finely crush the chocolate wafers in a food processor until it becomes a fine meal. In a large bowl, combine the wafer crumbs with the melted chocolate and blend until the crumbs are moistened. Reserve a heaping 1 cup crumb mixture in a small bowl. Press the remaining crumb mixture in the bottom and up the sides of a 9-inch diameter springform pan with 3-inch high sides. Freeze 1 hour.
For the glaze: In a large, heavy-bottomed saucepan, bring the cream and corn syrup to a boil over medium heat. Remove from the heat, add the chocolate and whisk until it melts. Set aside to cool until room temperature, about 1 hour.
For the filling: Quickly mix the ice cream, crushed candies and extract in a large bowl with a wooden spoon until blended. Put half the ice cream mixture onto the frozen crust and spread out. Evenly scatter the reserved cookie crumbs over the ice cream in the springform pan, pressing the crumbs down gently. Pour half of the chocolate glaze over the cookie crumbles and ice cream Freeze for about 3 hours.
When you about ready to repeat the layers, place the glaze back over low heat, just until pourable, but not warm. Remove the springform pan from the freezer and repeat with the remaining ice cream and glaze. Place back into the freezer for at least 3 hours or overnight.
Remove the cake from the freezer about 20 minutes before serving for easy removal of the springform sides. Release the pan sides and transfer the cake to a platter. Break off irregular pieces of the Candy Brittle and peel off the foil as you go. Press the brittle upright, candy side out, onto the top and sides of cake.
In a small, heavy bottomed saucepan over medium-low heat, cook the sugar, 3/4 cup water and corn syrup until the sugar dissolves. Increase the heat and boil, without stirring, until a candy thermometer registers 300 degrees F, about 15 minutes.
Place a 24-inch long sheet of foil on your work surface. Be extremely careful, the syrup is extremely hot. Pour the boiling syrup in wide zigzag lines across the foil. Working quickly and using an oiled offset metal spatula, spread the syrup evenly onto the foil, leaving a 1-inch border. Immediately sprinkle with all the candies, pressing the larger pieces into the syrup to make sure they stick. Be careful not to touch the syrup. Cool completely.
Put the candies in a zip top bag and crush with a rolling pin, or you can use a food processor to crush the candies Place your chef knife or your cake knife in a pitcher of warm water to help ease the cutting of your cake.