Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper and set aside.
Spread the crushed pretzels evenly on the prepared baking sheet, creating a single layer.
Bake the pretzels in the oven for about 5 minutes to slightly toast them, then remove and let cool.
In a microwave-safe bowl, combine the semi-sweet and milk chocolate chips. Microwave in 30-second intervals, stirring after each interval, until the chocolate is completely melted and smooth.
Pour the melted chocolate over the pretzels on the baking sheet, using a spatula to spread it evenly over the surface.
Sprinkle the toffee bits generously over the melted chocolate, followed by the chopped nuts if using.
Finish with a light sprinkle of sea salt flakes to enhance the flavors.
Place the baking sheet in the refrigerator for about 30 minutes or until the chocolate is fully set.
Once set, remove from the refrigerator and break the bark into pieces of your desired size.
Notes
Serve the bark in a decorative box or on a platter, garnished with a few extra toffee bits or nuts for added color and texture.