Crumble the cookies by hand into a measuring cup, then add to the food processor. Add the butter and sugar in and pulse until the texture is semi-smooth and evenly crumbly. Place into the center of a greased 9-inch round pie pan, and press across the bottom with your hands and up onto the sides. Either refrigerate the crust for 30 minutes before adding the ganache or be bake at 350°F for 10 minutes. If you bake it, leave the crust out to cool ahead of filling. In a pinch, you can purchase a premade tart crust instead.
In a small saucepan, bring the heavy cream to simmer. While it’s warming up, add the finely chopped chocolate to a medium-sized bowl. Once it reaches a simmer, immediately turn off the heat and pour the heavy cream into the bowl. Be careful not to let it boil. Let it sit for about five minutes.
Chop the room temperature butter into cubes and add it to the mixture. Now is the time to add the optional extract. An orange extract will go well with the garnish here, or you could instead use peppermint and garnish with fresh peppermint and/or crushed candy canes. Once everything is in, stir until super smooth. It will look super separated at first, with lots of fine bits of chocolate, but as you slowly mix, it will become dark in color and smooth.
Pour out the ganache into the crust. Scrape the remaining chocolate from the sides of the bowl using a spatula, and use the flat side of it to press any bubbles out and spread across evenly. Allow the tart to sit covered overnight at room temperature or in the fridge for 1-2 hours uncovered.
Layer the candied oranges alongside one side of the tart in a crescent moon shape. Layer under then over, creating a formation that gives the garnish some depth. Then add the chopped pistachios on top of the oranges for a bit of crunch. These topping will also give the dish a bold look because of all the varying colors and textures. Sprinkle with flake salt across the entire tart just before serving.
If you decide to use peppermint extract, simply top with fresh mint leaves and/or crushed candy canes. This option will give you a playful yet elegant, twist on holiday dessert.