Preheat the oven to 375 degrees. Line a 11 x 17 inch rimmed baking sheet with aluminum foil and spray with a neutral cooking spray, like coconut oil.

Spread the broken pretzels evenly over the prepared baking sheet.

In a small saucepan, melt butter and brown sugar together over medium heat, stirring constantly. Pay special attention to the outside bottom edges of the pan. Continue to stir and combine until you no longer feel any grainy sugar along the bottom of the pan. This will take about 4 minutes.

At this point, the mixture is likely already bubbling. If it's not, bring it to a gentle boil. Set a timer for 3 minutes and continue to simmer without stirring for 3 minutes. *Note: I highly recommend using a thermometer at this stage. You want the brown sugar mixture to reach a temperature between 280 and 290 degrees before pouring in on the pretzels. This can take slightly more or slightly less time than 3 minutes).

Pour the butter and sugar mixture over the pretzels. Place in the oven and bake for 5 minutes.

Place the pan on a cooling rack and immediately pour chocolate chips evenly over the top. Wait about 5 minutes then use a spatula or knife to spread chocolate evenly over the pretzel mixture. Sprinkle lightly with sea salt, if desired.

Let the toffee cool completely (this takes a few hours), then break into pieces and eat! (You can speed up the process by placing pan in the fridge or freezer.)