Prep the pan and oven: Heat oven to 325°F (163°C). Line the bottom of a 9-inch springform pan with parchment and lightly grease the sides.
Wrap the outside of the pan with foil to prevent leaks.
Make the crust: Stir almond flour, cocoa, sweetener, and salt. Add melted butter and vanilla and mix until it looks like damp sand. Press firmly into the bottom of the pan.
Bake 8–10 minutes until set. Cool while you make the filling.
Melt the chocolate: In a small saucepan, warm heavy cream until steaming. Remove from heat, add chopped chocolate, let sit 2 minutes, then stir until smooth.
Set aside to cool slightly.
Beat the cream cheese: In a large bowl, beat cream cheese on medium speed until smooth and fluffy, about 2 minutes. Scrape the bowl.
Add sweetener and sour cream: Mix in powdered sweetener and salt until combined, then blend in sour cream and vanilla. Keep speed low to avoid extra air.
Add eggs one by one: Beat in eggs one at a time, just until combined.
Do not overmix. Scrape the bowl once more.
Mix in the chocolate: Pour the melted chocolate mixture into the batter and stir on low until uniform and glossy.
Fill and smooth: Pour batter over the baked crust. Tap the pan gently on the counter to release bubbles.
Bake with a steam tray: Place the springform on a large baking sheet.
Put a separate pan of hot water on the lower rack to create steam. Bake 55–70 minutes, until the edges are set and the center jiggles slightly.
Cool gradually: Turn off the oven, crack the door, and let the cheesecake rest inside 30 minutes. Move to a rack and cool to room temp, then chill at least 6 hours, preferably overnight.
Make the salted caramel: In a heavy saucepan over medium heat, cook allulose, stirring often, until it melts and turns a light amber.
Whisk in butter. Slowly add warm cream (it will bubble), whisking until smooth. Off heat, stir in vanilla and salt.
Cool to a pourable consistency.
Finish and serve: Release the cheesecake from the pan. Pour cooled salted caramel over the top, letting some drip down the sides. Sprinkle with a touch of flaky salt and shaved chocolate if you like.
Slice with a hot, clean knife.