Prepare the crust: In a food processor, pulse the pistachios until finely chopped but not powdered. Combine with melted butter, honey (or maple syrup), and powdered sugar in a mixing bowl. Press the mixture into the base of a greased cake pan or springform pan. Place it in the fridge to set for at least 30 minutes.

1. Make the chocolate layer: In a heatproof bowl, combine the dark chocolate chips and heavy cream. Melt them together either over a double boiler or in the microwave, stirring until smooth. Add the vanilla extract and mix well.
2. Assemble the cake: Once the pistachio base has set, pour the melted chocolate mixture over it. Smooth the top with a spatula to ensure an even layer.
3. Chill the cake: Place the cake back in the fridge and let it chill for 3-4 hours, or until the chocolate layer is firm.
4. Serve: Once set, remove the cake from the fridge and carefully release it from the pan. Slice and serve chilled.