Preheat the oven to 350°F (175°C). Line the bottom of a 9-inch springform pan with parchment paper and lightly grease the sides.

In a bowl, whisk together the almond flour, granulated sweetener, and 1/4 teaspoon of the salt. Stir in the melted butter until the mixture resembles damp sand and holds together when pinched.

Press the crust mixture firmly and evenly into the bottom of the prepared pan, using the bottom of a glass to smooth and compact it.

Bake the crust for 10 to 12 minutes, until the edges are just beginning to turn light golden. Remove from the oven and let cool completely. Reduce the oven temperature to 300°F (150°C).

In a large mixing bowl, beat the softened cream cheese and 3/4 cup powdered sweetener until completely smooth and creamy, scraping down the bowl as needed to remove any lumps.

Add the sour cream, vanilla extract, and remaining 1/4 teaspoon salt. Beat again until the mixture is glossy and uniform.

Add the eggs one at a time, mixing on low speed just until each egg is incorporated. Do not overmix to avoid incorporating excess air.

Pour the cheesecake batter over the cooled crust. Tap the pan gently on the counter several times to release any surface bubbles, then place the pan on a rimmed baking sheet.

Bake the cheesecake at 300°F (150°C) for 45 to 55 minutes, until the edges look set but the center still has a slight wobble about the size of a small coin when you gently jiggle the pan.

Turn off the oven and crack the door open with a wooden spoon. Leave the cheesecake inside for 30 to 45 minutes to cool gradually.

Transfer the pan to a wire rack and cool to room temperature. Once cooled, cover and refrigerate for at least 4 hours, preferably overnight, until fully chilled and firm.

When the cheesecake is fully chilled, prepare the banana pudding layer. Sprinkle the gelatin over the cold water in a small bowl and let it bloom for 5 minutes.

In another small bowl, whisk together the egg yolks, 1/3 cup powdered sweetener, and a small pinch of salt until smooth and slightly lightened.

In a small saucepan, heat the heavy cream over medium-low heat until it is steaming and just beginning to simmer around the edges, but not boiling.

Slowly pour the hot cream into the egg yolk mixture while whisking constantly to temper the yolks.

Pour the tempered yolk mixture back into the saucepan and cook over low heat, stirring constantly with a spatula, until the custard thickens slightly and coats the back of the spatula, 3 to 5 minutes. Do not let it boil.

Remove the custard from the heat. Stir in the bloomed gelatin until completely dissolved.

Whisk in the mashed banana and banana extract, tasting and adjusting the extract as needed for a strong banana flavor. Let the mixture cool, stirring occasionally, until it reaches room temperature and is slightly thickened but still pourable.

Gently pour the cooled banana pudding mixture over the chilled cheesecake, smoothing the top with an offset spatula if needed.

Refrigerate the assembled cheesecake for at least 2 hours, or until the banana pudding layer is fully set and the top is firm to the touch.

To serve, run a thin knife around the inside edge of the pan, release the springform ring, slice with a hot, clean knife, and serve well chilled.