Preheat oven to 400° Fahrenheit and line a large baking sheet with aluminum foil. Arrange the pretzels in an even layer on the baking sheet.
Melt butter and sugar in a small saucepan over medium heat, stirring frequently. Once the butter has melted, cook the toffee for another 4-5 minutes, stirring constantly until dark brown and bubbling.
Remove from the heat, whisk in the vanilla extract then immediately slowly and evenly pour the toffee over the pretzels. Place the pretzels and toffee in the oven and bake for 5 minutes.
While the bark bakes, melt the chocolate in the microwave or over a double boiler until completely smooth. Remove the pretzels and caramel from the oven, let them cool for 1-2 minutes or until no longer bubbling, then slowly pour the melted chocolate over top of the toffee and gently spread into an even layer.
Leave the chocolate toffee pretzels bark to cool at room temperature for about 30 minutes, then transfer to either the fridge for 6 hours or the freezer for 3 hours. Remove the bark from the pan, peel away the foil, and break into large chunks.
Notes
The nutritional info for this recipe was calculated using gluten-free pretzels, non-dairy butter, coconut sugar, and extra dark chocolate chips.