Break the milk chocolate and white chocolate into pieces, place in two separate thin-sided bowls. One after the other, suspend the bowls over a gently simmering bain-marie; the bowl must not touch the water. Melt the chocolate, remove from the heat, stir the chocolate until smooth.
Dip half of the salted pretzels in each of the bowls of chocolate, mix. Using two forks, place the pretzels on two sheets of baking paper.
Before the chocolate sets, sprinkle the pretzels with pistachios, raspberry powder or chocolate sprinkles, leave to dry.