Place the sugar and water in a small pot. Bring the mixture to a boil, swirling the pot to dissolve the sugar crystals. Boil for 2 – 3 minutes on high heat then remove the pot from heat. Let cool to room temperature before stirring in the rum.
Chocolate Genoise (step-by-step photos here)
Preheat the oven to 180 degrees Celsius. Grease 2 9-inch square baking trays and line the bottom with parchment paper. Set aside.
Sift the flour and cocoa powder together thrice. Set aside.
Place the eggs in a medium pot or a large metal mixing bowl. Add in the sugar and whisk immediately until combined. You must whisk the sugar immediately into the eggs otherwise lumps will form and it will be very hard to get rid of them later on.
Hold the pot / mixing bowl over medium-low heat and whisk the egg-sugar mixture constantly, to bring up the temperature until its like baby’s milk – warm but not hot. The mixture would be foamy. You can set it directly over the heat, just make sure that you remove it from time to time so you don’t end up with cooked eggs.
Transfer the mixture in the pot into a mixing bowl and whisk it with a hand-held electric mixer on high speed until the bubbles start to disappear. The mixture will triple in volume. Turn the mixer down to low and whisk it for at least 1 minute, to stabilize the air bubbles in the cake batter. The cake batter will leave a trail when you lift up the beaters and will sink and merge back slowly into the batter.
Sift in half of the flour mixture and gently fold it in until almost all are combined. Sift in the remaining half of the flour mixture and fold until no flour pockets are visible. Do not over-mix.
Add one-third of the cake batter into the hot, melted butter. Use a smaller spatula and fold the butter into the cake batter thoroughly. Pour the butter-mixed batter back into the rest of the cake batter and fold in gently.
Divide the cake batter between the trays. Tilt the trays so the batter spreads out evenly and drop it once on the counter top to burst the uneven air bubbles.
Bake in the middle rack for 10 to 12 minutes until the cake springs back when touched gently and a skewer inserted into the centre of the cake comes out clean. Leave it to cool completely.
Assembly
Get 9 1/2-cup ramekins (3-inch base) and line the insides with plastic wrap, leaving an overhang. Set aside.
Use a 3-inch cookie cutter (that is the same size as the bottom of the ramekin) and cut out genoise rounds. You should get 18 rounds.
Brush both sides of one genoise round with the Rum Sugar Syrup and lay it on the bottom of the ramekin. Repeat until all the ramekins are lined with one genoise round.
Scoop the ice cream into a large mixing bowl and leave it to softened slightly. Place the Oreo cookies in a large ziploc bag and crushed them with a rolling pin - don't crush them into smithereens, leave some large chunks in for texture. Dump the crushed Oreos and chocolate sauce into the softened ice cream and fold with a rubber spatula until fully mixed. Divide the ice cream mixture among the 9 ramekins.
Brush both sides of the remaining genoise rounds and place on the ramekins. Press down gently. Wrap the cake with the plastic wrap and freeze for at least 4 hours.
Chocolate Glaze
Stove method: Place the chopped chocolate in a heat-proof bowl. Place the heavy cream in a small pot and heat over medium heat until the heavy cream comes to a simmer (small bubbles appear on the sides of the pot). Pour the hot cream onto the chocolate and let it stand for 1 minute. Stir the mixture until all the chocolate has melted and the mixture is smooth. Stir in the golden syrup. Add more syrup until it’s of a consistency that you like (I like the glaze to be quite runny, so I use more than double the amount of syrup). Let it cool slightly.
Microwave method: Place the heavy cream in a microwave-safe bowl (glass or ceramic). Microwave the cream on medium for 30 seconds until the cream is hot. Add in the chopped chocolate and stir – the chocolate will start to melt. Place the bowl back into the microwave and microwave for 10 seconds. Stir the mixture and if there’s any remaining un-melted chocolate, repeat the process (do not microwave for too long at one go unless you want to burn your ganache). Stir in the golden syrup. Add more syrup until it’s of a consistency that you like. Let it cool slightly.
Unmould the ice cream cakes and place it on serving plates. Pour the chocolate glaze over the ice cream cakes (or transfer the chocolate glaze into a small serving pot for the guests to add as much sauce as they like). Serve immediately.