Preheat the oven to 350°F and line an 8x8 inch baking pan with parchment paper, leaving an overhang on two sides. Stir the almond flour, cocoa powder, powdered sweetener, salt and melted butter until it looks like wet sand, then press firmly into the pan.Bake the crust for 10 minutes, then set it aside and reduce the oven to 325°F.
Beat the cream cheese and powdered sweetener until completely smooth. Mix in the pistachio butter, sour cream and vanilla, then add the eggs one at a time on low speed just until combined.
Pour the pistachio filling over the crust and smooth the top. Bake for 28 to 32 minutes, until the edges are set and the center still has a slight jiggle, then cool at room temperature for 1 hour.
Melt the butter in a skillet over medium heat and toast the shredded coconut and chopped pistachios for 3 to 4 minutes, stirring constantly, until golden. Remove from the heat and stir in the pistachio butter, tahini and powdered sweetener.
Spread the crunch mixture evenly over the cooled cheesecake and press it down gently with the back of a spoon.
Heat the heavy cream until steaming, pour it over the chocolate chips and let it sit for 2 minutes, then stir until glossy. Spread the chocolate over the crunch layer and sprinkle with the remaining chopped pistachios.
Chill for at least 4 hours, then lift the slab out using the parchment and slice into 16 bars.