1. Preheat the oven to 350 degrees F (175 degrees C). Grease the sides of a 9 inch spring form pan. In a medium bowl, mix together the vanilla wafer crumbs, ground walnuts, and melted butter. Press into the bottom of the prepared pan.

2. In a large bowl, stir cream cheese to soften. Mix together 1 1/8 cup sugar and flour; stir into the cream cheese until smooth. Stir in eggs, one at a time, mixing until well blended after each one. Stir in sour cream, mashed banana, banana liqueur, and 1 1/2 teaspoons of vanilla. Pour over the crust in the spring form pan.

3. Cover the bottom of the outside of the cheesecake pan with aluminium foil to prevent water from the water bath from seeping in. Place spring form pan inside a larger pan. Place the whole thing into the preheated oven, and fill the outer pan with hot water.

4. Bake for 45 minutes in the preheated oven. After the time is up, turn the oven off, but leave door closed. Leave cheesecake in the unopened oven for 1 hour. Before removing from the water bath. Run a knife around the outer edge of the cake to keep it from shrinking away from the centre and cracking. Let cool to room temperature, then refrigerate until chilled, at least 3 hours, or overnight.

5. In a small bowl, sprinkle the unflavoured gelatine over the cold water, and set aside to soften. Heat milk in a small saucepan over medium-low heat until hot but not boiling. Meanwhile, whisk together 1/3 cup sugar and egg yolks until smooth and frothy. Whisk about 1/3 of the hot milk into the egg yolk mixture, then pour the yolk mixture into the pan with the remaining milk. Cook over low heat, stirring constantly with a spatula, making sure that the mixture does not burn on the bottom, until it is thick enough to coat the back of a metal spoon. Remove from the heat. Stir the softened gelatine into the hot pastry cream until dissolved, then stir in vanilla. Pour into a bowl, place a sheet of plastic wrap directly on the surface, and refrigerate until cooled, about 1 hour.

6. When the pastry cream is cooled, whip heavy cream just past soft peaks. Stir pastry cream to soften, then fold in the whipped cream. Place vanilla wafers on top of the cooled cheesecake, then spread the vanilla cream over the entire top. Chill until serving. Run a wet knife around the outer edge of the cake before removing the sides for a cleaner look.