Step 1: Using an air popper or stove top, pop popcorn. (or alternately in the microwave if using microwave bags of popcorn) following directions. Remove any un-popped popcorn kernels. Place in large bowl.
Step 2: Toss in broken pretzel pieces and M&Ms (you can set some aside to sprinkle on at the end if you want them to show through better).
Step 3: In a microwave safe bowl, melt white chocolate melting wafers in 30 second intervals, stirring after each interval until melted and smooth. Remember that the chocolate will continue to melt after removing from microwave.
Step 4: Drizzle half of melted chips over popcorn mixture, then stir, tossing gently a few times with a rubber spatula. Then drizzle remaining half of melted chips over popcorn. Gently stir mixture until evenly coated (don’t over stir though or your sprinkles won't stick if the white chips begin to set and harden).
Step 5: Pour mixture into a single layer onto wax paper or parchment paper (or into cookie sheets lined with the paper). Sprinkle entire mixture evenly with sprinkles before melted white chocolate starts to set. Allow to cool and harden, then gently break into pieces and store in an airtight container.