Line a baking sheet with parchment paper and set it aside.
Place the dark chocolate chips in a microwave-safe bowl and heat in 30-second intervals, stirring between each, until fully melted and smooth.
Spread the melted dark chocolate evenly across the parchment paper to form a thin rectangle.
Place the white chocolate chips in a separate microwave-safe bowl and heat in 30-second intervals, stirring between each, until melted and smooth.
Drizzle the white chocolate over the dark chocolate in a loose spiral pattern.
Drag a toothpick from the center outward through the white chocolate lines to form a spiderweb design.
Scatter the broken pretzels evenly across the surface while the chocolate is still soft.
Let the bark sit at room temperature until firm, then break it into pieces.