If you are using a regular blender or food processor, place half the pistachios in the blender first and pulse until they have turned a fine powdery consistency. Add the remaining pistachios and process again. They will turn into a powder first, then into a smoother paste the longer you blend them. Add the melted coconut oil and stevia and blitz until all the ingredients are smooth, with only a few grains left.
Pour into a small bowl and freeze for about twenty minutes while you make the chocolate coating.
Line a freezer-safe dish or platter with baking parchment. Remove the pistachio filling from the freezer. Using a teaspoon (a melon scooper might work, too) scrape a walnut-sized amount of filling. Roll into a small ball in your hands, and place on the baking parchment. Repeat this process to create 9 truffles.
Freeze the truffles for another five minutes.
Place a small saucepan over low heat. Gently warm up the coconut oil, turn the heat really low, then add the chocolate and slowly let it melt. Stir occasionally to prevent burning. When the chocolate has become silky, stir in the stevia, then take off the heat.
Let it cool. Stir briefly before coating the pistachio balls into the chocolate, just to keep it manageably liquid. Dip each pistachio ball into the chocolate liquid, coating it well, then place back onto the baking parchment. Repeat this process for every single ball.
NOTE: This makes a lot of chocolate, but you need that to be able to fully dip in your pistachio truffles. And you'll have leftovers to make hot chocolate, perhaps to go with your truffles, if that's not overdosing on chocolate for you.
Pistachio Drizzle (optional)
Reserve a teaspoon of the wet pistachio filling. Place it in a small saucepan, along with a teaspoon of coconut oil, and melt the two together. Set aside to cool a little. When the truffles are coated with chocolate and have set, drizzle the pistachio liquid over them and freeze again.