Preheat the oven to 325°F (165°C). Grease a 9-inch springform pan, line the bottom with parchment paper and line the sides with a tall strip of parchment.
Whisk together the almond flour, coconut flour, granulated sweetener, baking powder and salt. Add the melted butter, eggs, sour cream and vanilla extract and stir until a smooth, thick batter forms.
Spread the batter evenly in the springform pan. Bake for 18-22 minutes, until golden and a toothpick comes out clean. Let the cake cool completely in the pan.
Sprinkle the gelatin over the cold water and set aside to bloom. Heat 1 cup heavy cream with the almond milk in a saucepan until steaming but not boiling.Whisk the egg yolks with the powdered sweetener, then slowly pour in the hot cream while whisking constantly. Return everything to the saucepan and cook over low heat, stirring constantly, for 4-6 minutes until the custard coats the back of a spoon. Do not let it boil.
Remove from the heat and stir in the bloomed gelatin and vanilla extract until fully dissolved. Strain into a large bowl and cool for 25-30 minutes, stirring now and then, until room temperature but still liquid.
Whip the 1 1/2 cups cold heavy cream to medium peaks. Fold it into the cooled custard in three additions until smooth and airy. Pour over the cake in the springform pan and refrigerate for at least 4 hours, until fully set.
For the ganache, heat the heavy cream until just simmering and pour it over the chocolate chips and butter. Let it sit for 2 minutes, stir until glossy and cool for 10 minutes.
Pour the ganache over the set Bavarian cream and tilt the pan to cover the surface. Chill for 30 minutes, then release the springform, peel away the parchment and serve.