Get Your Crust Ready: First, put the ½ cup of pistachios into a food processor and pulse them until they look like fine crumbs. In a medium bowl, mix together the almond flour, ground pistachios, sugar-free sweetener, and salt. Pour in the melted butter, egg yolk, vanilla extract, and a tiny drop of green food coloring if you're using it. Stir everything until a soft dough forms. Press this dough evenly into the bottom of an 8x8 inch baking pan lined with parchment paper. This makes it super easy to lift out later!
Whip Up the Creamy Pistachio Filling: Clean out your food processor. Now, blend the other ½ cup of pistachios with the avocado oil until it becomes a relatively smooth pistachio butter. Add the room temperature cream cheese, about ¼ cup at a time, blending well after each addition until it's super smooth. Stir in the Greek yogurt and blend again until well combined. Next, add the powdered sugar-free sweetener and salt, blending until everything is smooth and incorporated. Finally, add the egg, vanilla extract, almond extract, and another drop of green food coloring if you like. Blend just until smooth – try not to overmix once the egg is in there!
Bake and Chill: Carefully pour the creamy pistachio filling over your prepared crust in the pan. Bake in a preheated oven at 325°F (160°C) for about 22 minutes. The filling should be mostly set but still a little soft in the center. Let the bars cool completely to room temperature before moving on. This is important for a smooth topping!
Make the Chocolate Topping: Heat the heavy cream in a small saucepan on the stovetop or in the microwave until it's hot but not boiling. Pour the hot cream over the sugar-free chocolate chips in a bowl. Let it sit for a minute, then stir until the chocolate is fully melted and you have a smooth, glossy ganache.
Finish and Enjoy! Pour the chocolate ganache evenly over the cooled pistachio bars. Spread it gently with a spatula. For a fancy look, you can pipe thin stripes of green icing (made from melted sugar-free white chocolate + cream + green food coloring) across the ganache, then drag a toothpick through them in the opposite direction for a cool design. Sprinkle the chopped pistachios around the edges for extra crunch and color. Refrigerate the bars for several hours, or until the chocolate layer is completely firm. Once chilled, lift the bars out of the pan using the parchment paper and slice them into 16 neat squares using a sharp knife. Store any leftover bars in an airtight container in the fridge.