Top the pretzels with the white chocolate melts and place on a microwave safe plate. Microwave on 50% (I found that the defrost setting also works well) until the chocolates are melted.
Carefully remove the plate (it might be hot!).
Place a single M&M in the center of each melt and press it down just slightly. Add 6-7 more candies around the edges.
Place the plate into the fridge until the candies are set. You can also leave them out at room temperature to set, but they'll take a little longer to do so.