Break up the pretzels and set aside.
Unwrap the chocolate bars and break them up into separate microwave safe bowls.
Melt the semi-sweet chocolate first. Start with one minute on high, remove and stir and return for 30 seconds on high. Remove and stir. Repeat until the chocolate is melted smoothly.
Next, melt the white chocolate, starting with one minute on high. Remove and stir, return for 30 seconds and stir again. Repeat until smoothly melted.
Once the white chocolate is melted, add the peanut butter to it and stir until well blended.
Add half of the broken pretzels to each bowl of chocolate and stir until the pretzels are completely coated.
Line a medium sized baking sheet with wax paper. Pour out the chocolate in an alternating pattern, like a checker board.
Swirl the back of a butter knife back and forth in the chocolate to marblize and mix the flavors.
Place the baking sheet in the fridge for at least an hour, or until firm.
Once firm, break apart the bark into smaller pieces and store in an airtight container in the fridge.
