Spread the cookie and pretzel pieces evenly onto the mat or wax paper.
Melt the white chocolate – either in the microwave* or over a double boiler – until smooth and fully melted. (*Anytime you melt chocolate in the microwave, it’s best to heat the chocolate in 30-second time increments, then stop to stir the chocolate before heating it more. Chocolate melts very quickly in the microwave and it can easily burn!)
Drizzle the melted chocolate over the cookie-pretzel mixture, making sure it evenly coats the cookie and pretzel pieces. If necessary, use a spatula to evenly spread the melted chocolate.
While the chocolate is still wet, sprinkle the candy pieces and sprinkles evenly over the chocolate, pushing the candy down a bit if necessary to make sure that it is embedded in the melted chocolate.
Let cool until the chocolate firms up. Peel the bark from the Silpat mat or wax paper and break into small pieces.