Preheat the oven to 375° and line a sheet tray with parchment paper. Line the pretzels in a single layer on the parchment paper.
In a small saucepan, melt the butter over medium/low heat.
Once melted, add in the sugar and stir well using a wooden spoon. Stir constantly until the mixture comes together and starts boiling. Insert a candy thermometer and boil until mixture reaches 270°, stirring regularly. This took exactly 5 minutes for me every time.
Take off the heat and quickly pour over the pretzels, covering as much as possible. Place the pan in the oven for 5 minutes.
Remove from the oven and stir with the wooden spoon to coat all the pretzels and try to arrange them in a single layer again. Sprinkle the chocolate chips on top evenly and place back in the oven for 1 minute. Remove and use the spoon to spread all over the pretzel/toffee mixture.
Sprinkle with flaky salt if desired. Place in the fridge for an hour to set.
Remove and break into pieces.
Store covered at room temperature. Share with friends, or savor these delightful treats on your own.