Preheat the oven to 325°F (160°C). Grease a 9-inch (23cm) springform pan and wrap the outside of the pan with aluminum foil to prevent water from seeping in during the baking process.
In a small bowl, mix together the vanilla wafer cookies and melted butter until the crumbs are moistened. Press firmly onto the bottom of the prepared pan and bake for 8-10 minutes. Remove from oven and let cool.
In a large mixing bowl, beat the cream cheese at medium speed until creamy and smooth. Add the sugar and heavy cream; beat until combined. Add the eggs, one at a time, beating well after each addition. Stir in vanilla extract.
Stir in the mashed bananas and pour the mixture over the cooled crust.
Place the springform pan inside a larger roasting pan. Fill the roasting pan with hot water until it reaches halfway up the sides of the springform pan.
Bake for 1 hour and 30 minutes or until the cheesecake is set, but still slightly jiggly in the center.
Turn off the oven and let the cheesecake cool inside the oven with the door slightly ajar.
In a small saucepan, combine the sugar, water, and dried lavender flowers. Bring to a boil and stir until the sugar has dissolved. Remove from heat and let steep for 10 minutes. Strain out the lavender flowers and stir in the fresh lemon juice.
Let the syrup cool to room temperature, then pour over the cheesecake. Chill the cheesecake in the refrigerator for at least 4 hours or overnight