1. Let ice cream stand at room temperature until spreadable, about 10 minutes.
1. In top of a double boiler or metal bowl set over saucepan of simmering water, melt butter, sugar, and cocoa powder until smooth, about 3 minutes. Remove from heat. In a large bowl, beat egg. Slowly whisk in stovetop mixture (to temper egg) until smooth. Stir in coconut and graham cracker crumbs; set aside.
1. In large bowl and using an electric mixer, beat butter, custard powder, and 35% cream until light and fluffy. Beat in icing sugar in 2 additions until combined. Cover with plastic wrap and set aside.
1. In a microwave safe bowl, melt chocolate and butter on low, for about 1 minute, stirring once or until melted.
2. Meanwhile, line an 8-inch loaf pan with plastic wrap, leaving a 3-inch overhang on all sides. Press base into bottom of pan. Spoon half of the ice cream on top of base; spread evenly. Freeze along with remaining ice cream for 15 minutes.
3. Spread custard filling over ice cream. Freeze for 15 minutes. Spread with remaining ice cream. Cover with plastic wrap and freeze until firm, about 3 hours.
4. Spread chocolate topping over ice cream. Return to freezer until firm, about 15 minutes.
5. To serve log, using plastic wrap overhang as handles, remove from loaf pan. Remove plastic wrap and place on serving platter. Cut into 1-inch thick slices using a hot knife. Serve.