Melt white chocolate chips with shortening in a LARGE bowl in the microwave on HALF POWER for 60 seconds. Stir. Repeat until melted. (Mine took 2 minutes.)
Add the Chex cereal to the melted chips & fold gently.
In a gallon size zip-top bag combine, muffin mix, powdered sugar, cinnamon & nutmeg. Add the white chocolate coated cereal, zip the bag shut & shake until everything is covered with the dry mixture.