Preheat the oven to 350F and line an 8x8 inch pan with parchment paper, leaving overhang on two sides. Melt the butter and 3 oz of dark chocolate together in a microwave safe bowl in 30 second bursts, stirring until smooth.
Whisk the allulose into the warm chocolate mixture, then add the eggs one at a time, whisking well after each. Whisk in the vanilla. Beat the batter vigorously for one full minute so it turns glossy and slightly thickened.
Fold in the almond flour, cocoa powder and salt until just combined with no dry streaks. Spread the batter evenly into the pan and bake for 22 to 25 minutes, until the edges are set and the center is still slightly soft.
While the brownies bake, toast the shredded coconut with 2 tbsp butter in a skillet over medium heat, stirring constantly for 4 to 5 minutes until deeply golden and crispy. Transfer to a bowl and let cool for 5 minutes.
Stir the pistachio butter, powdered allulose and chopped pistachios into the toasted coconut until everything is coated and forms a thick, crunchy mixture.
Let the brownies cool in the pan for 15 minutes, then spread the pistachio crunch layer evenly over the top, pressing gently with the back of a spoon. Chill for 20 minutes to firm up.
Melt the remaining 3 oz dark chocolate with the coconut oil until smooth. Pour over the pistachio layer and tilt the pan to cover evenly. Sprinkle with chopped pistachios.
Refrigerate for at least 1 hour until the chocolate is set. Lift out using the parchment overhang and cut into 16 squares. Store in the fridge for up to 5 days.