For the pastry:
In a food processor, gently mix the flour, cocoa, sugar, and butter until the mixture is barely crumbly.
Add enough banana nectar so that the mixture holds together.
Remove from the processor and form a ball.
Flatten slightly, wrap in plastic film, and refrigerate for 30 minutes.

Remove the pastry from the refrigerator and roll out on a floured surface to 1/4″ (5mm) thickness. Place in a 9″ (23cm) tart mold with a removable bottom. Prick the bottom.

Place a sheet of parchment paper or aluminum foil on the pastry and cover with dried beans or rice.
Bake in a preheated oven at 350F (180C) for 10 minutes.
Remove the beans and bake for an additional 10 to 15 minutes, or until the crust is cooked through. Let cool.

For the coconut cream pastry cream:
Bring the milk and coconut milk to a boil in a small saucepan.

Meanwhile, whisk the egg yolks with the sugar and cornstarch until the mixture is smooth.
While mixing, slowly pour in the hot milk and return the mixture to the saucepan.
Return the saucepan to the heat and bring to a boil, stirring constantly, until thickened.
Add the cinnamon, nutmeg, vanilla extract, and butter.
Mix well and let cool, covering the saucepan with plastic film.

For the garnish:
Whip the 35% cream into whipped cream, adding the powdered sugar and vanilla extract.
Fold the sour cream into the whipped cream using a spatula. Reserve.

Assembly:
In the tart shell, arrange the sliced bananas.
Cover with the coconut cream pastry cream, then the whipped garnish.
Refrigerate until serving.