Make the cannoli filling! To do this, simply add the ricotta, powdered sugar, 1/2 tsp of tangerine zest (just zest some of the tangerines you'll be using for later), chocolate chips, and pistachio nuts to a medium bowl and stir to combine.
Lay the pre-rolled pie dough out on a baking sheet or some parchment paper. Then add all the cannoli filling to the center, leaving an inch or 2 of dough to fold over once you're done.
Peel the tangerines and separate them into individual slices. Place those slices atop the cannoli filling in a spiral formation, making sure to cover it all. Once you're done, fold the edges of the crust over the tangerines and cannoli filling, pressing down to make sure that it sticks together. Then brush the crust with the beaten egg. Put the butter slices on top of the tangerines, throw a few more chopped pistachios on top if you feel like it, and transfer the whole galette to the fridge to chill for about 30 minutes.
Preheat the oven to 400° Fahrenheit while the galette is in the fridge.
Once it's chilled, put the galette in the oven for about 45 minutes, or until the crust is golden and the filling is is a little bit bubbly.
Transfer the galette to a cooling rack, and let it hang out for about 20 minutes before cutting into it.