Preheat your oven to 350 degrees F. Spread the pistachios on an ungreased baking sheet. Bake until the pistachios smell toasty and fragrant, about 5 minutes. DO NOT WALK AWAY, and keep a close watch on them so that they do not burn. Once the pistachios are toasted, immediately remove them from the baking sheet to a bowl or plate so that they do not continue to toast and burn on the hot baking sheet.
If the dates are hard or dry, place them in a bowl and cover with boiling water to rehydrate. Let sit 10 minutes, then drain and pat dry.
Place the walnuts and 3/4 cup of the toasted pistachios in a food processor. Pulse until the nuts reach the consistency of a meal. Remove from the food processor and set aside.
Place the remaining 1/4 cup pistachios in the food processor, then pulse until they are as crushed as you would like them to be for sprinkling on top (I left mine somewhat coarse). Remove to a separate plate or bowl and save for topping the truffles.
Place the pitted dates in the food processor. Pulse in long bursts until the dates form a sticky paste and only small bits remain (the dates may form a ball that sticks to the side). Add the cocoa powder, vanilla extract, salt, and 1/2 cup of the ground walnut-pistachio mixture. Pulse a few times to incorporate. Continue adding the ground nuts a few tablespoons at a time until you have a loose, malleable "dough" that can be scooped and pressed into balls.
Line a baking sheet with parchment paper. With a small scoop or spoon, scoop a portion of the dough, then roll it into a ball with your hands, pressing lightly as needed so that the ball holds together. Place the ball on the baking sheet. Repeat with remaining dough. (You will have about 12 truffles total, depending upon how large you roll them.) Place in the freezer and allow them to firm up for 10 to 15 minutes.
Meanwhile, place the chopped chocolate in a heatproof bowl, then set that bowl over a pan of simmering (not boiling) water. Make sure that the bottom of the bowl and the water do not touch. Melt the chocolate, stirring often. When the chocolate is almost completely melted but you can still see a few pieces, remove the bowl from the pan. Add the coconut oil and stir until smooth and glossy, letting the residual heat of the chocolate melt the mixture the rest of the way.
Remove the truffles from the freezer. Working one at a time, dip a truffle into the melted chocolate. Use two forks to roll it around so it's coated, then use the forks to remove the truffle from the chocolate and lightly tap away any excess chocolate. Place the truffle on the parchment paper, then top immediately with some of the reserved chopped pistachios. Be sure to sprinkle it right away—the chocolate sets fast! Repeat with the remaining truffles. Let sit at room temperature for a minute or two to set. Enjoy!
TO STORE: Store leftovers in an airtight container in the refrigerator for 2 weeks or at room temperature for 1 week.
TO FREEZE: Place truffles in an airtight freezer-safe storage container in the freezer for up to 3 months. Set out at room temperature for a few minutes prior to serving.