Preheat oven to 350°F. Grease and flour two 9 inch round, 2 inch deep metal pans. If your pans are dark (black), use 325 degrees F.
In a mixing bowl, stir together sugar, flour, cocoa, baking powder, baking soda and salt. Add egg, milk, oil and vanilla; stir until well mixed. Stir in boiling water (batter will be thin), and stir until mixed. Batter maybe have a few lumps in it, Pour batter into prepared pans (unless you doubled it, the layers should be very thin) and bake for 20 minutes or until wooden pick inserted in center comes out clean.
Let cool 10 minutes; remove from pans and let cool on a wire rack.
Line the inside of one of the round pans (make sure it’s cool) with plastic wrap. Put one of the cake layers in the lined pan and put in the freezer while you make the ice cream.
To make the ice cream, beat 1 cup of the cream in a mixing bowl with a handheld electric mixer until stiff peaks form. In a second bowl, beat together the remaining 2 tablespoons of cream, 2 tablespoons of milk, 7 ounces (⅔ cup) condensed milk (weigh it out if you can) and vanilla extract. Fold in the whipped cream and about half of the chopped Oreos. Pour this mixture over the cake that’s in the lined pan. Return to freezer and freeze for 4 hours or until very firm
Prepare the fudge sauce. Combine the chocolate chips and condensed milk in a small saucepan and heat over medium low, stirring gently to melt the chips. Remove from heat and stir in the butter. Stir until butter melts. Add the water and vanilla. Let mixture cool to room temperature. Spread the room temperature fudge sauce over the firm ice cream, then scatter remaining Oreos over the fudge sauce. Cap with the other layer of cake and put everything back in the freezer overnight or until very solid.
Put the cream in a bowl and whip until stiff peaks start to form. Beat in the sugar and vanilla.
Lift the cake from the pan by pulling up the plastic wrap and spread cream mixture all over the cake. Put the cake back in the freezer until your whipped cream icing is firm. To serve, set on a cake platter and decorate with chocolate syrup, chocolate flavored or regular sweetened whipped cream. Sprinkle crushed Oreos in the center.
Let the cake stand for about 10 minutes before you cut it, or cut it and let the cut pieces stand for a few minutes before serving.