Preheat oven to 350 degrees F, and line a large rimmed baking sheet with parchment paper. Add pretzel sticks to baking sheet, spreading in an even layer. Remove any pretzels that won't fit, and set pan aside.
Add butter and maple sugar to a medium sauce pan, and heat on medium. Stir frequently until butter melts, then increase heat slightly to bring mixture to a soft boil. Once boiling, cook for 3-5 minutes, stirring frequently, until caramel begins to foam and thicken.
Remove from heat, and stir in vanilla and cinnamon. Immediately drizzle caramel over pretzel pieces. Start at one end of the pan, and drizzle back and forth in a steady stream, covering as many of the pretzels as you can.
Transfer pan to the preheated oven, and bake for 8-10 minutes, until caramel thickens, bubbles up, and distributes throughout the pan.
Remove pan from oven and sprinkle chocolate chips evenly over the top of hot toffee. Transfer the pan back to the oven for another 2 minutes, or until chocolate begins to melt.
Remove pan from oven, and use a spatula to spread chocolate into an even layer. Sprinkle with flaky sea salt and let rest on a wire rack until cool.
Once cool enough to handle, transfer to the refrigerator to finish setting. To speed things up, you can transfer pan to the freezer.
Break into pieces and enjoy. Stored in an airtight container bark will keep at least 4-5 days, if it lasts that long!