Preheat the oven to 350 degrees. Line a 12-cup muffin pan with foil liners and lightly spray with cooking spray.
For the crust, combine the graham cracker crumbs, flour, sugar, and cinnamon in a medium bowl. In another bowl, mix the melted butter, vanilla, and mashed banana. Add the butter mixture to the graham cracker mixture, and stir with a fork to moisten most crumbs. Press about 1 scant tablespoon of crumb mixture into the bottom of each muffin cup; use the chunkier crumb pieces here and reserve the leftovers to sprinkle on top later. Bake at 350 degrees for 12 minutes. Remove to a wire rack.
For the filling, use an electric mixer on high speed to beat the ricotta, sour cream, vanilla, and sugar in a large bowl until very smooth, about 2 minutes, scraping down the sides of the bowl a couple of times. Beat in the egg. Fold in the mashed banana until just incorporated. Fill each muffin cup with ricotta mixture. Sprinkle a little of the reserved crumb mixture on top of each cheesecake.
Bake 25–30 minutes (the cakes should reach 160 degrees). Transfer to a wire rack and let cool about 30 minutes, then transfer to refrigerator to chill for at least one hour before serving (the texture is ideal when they are chilled all the way through).
To serve, make the topping by combining the heavy cream and vanilla in a large bowl. Beat on high speed with an electric mixer. As the cream gains a little volume, sprinkle in the sugar and continue beating until the cream holds soft peaks (the whole process should take about 2 minutes).
Remove the foil liners from the cheesecakes and place the cakes on a serving platter or on individual plates. Place a dollop of whipped cream on each cheesecake, insert a banana slice, and sprinkle lightly with nutmeg. Pass leftover whipped cream at the table in case anyone wants extra.