Place the Rice Chex in a very large mixing bowl. Set a large zip-top bag or second bowl nearby for the powdered sugar step.
Melt the white chocolate in 20-second microwave intervals, stirring after each, until almost completely melted. Stir until smooth, then immediately mix in the pistachio cream, lemon zest, almond extract, and salt.
Pour the pistachio-white-chocolate mixture over the cereal and fold gently until evenly coated.
Transfer the coated cereal to the zip-top bag or keep it in the bowl. Add the powdered sugar and finely chopped pistachios and shake or toss until every piece is lightly coated.
Spread on a parchment-lined baking sheet in a single layer and let sit for about 20 minutes, until the coating feels dry. Break apart any larger clusters before serving.
Notes
Work gently when coating the cereal so the Chex stays crisp and intact.