Preheat the oven to 375°F/190°C. Line a rimmed baking sheet with foil and spray with cooking spray or use a silicone baking mat. Cover the bottom of the pan in a single layer of broken mini pretzels or Snaps pretzels. Set aside.
In a small or medium saucepan, stir the butter and brown sugar to combine. Let come to a rolling boil over medium heat and cook for 3 minutes with NO stirring. Pour the hot toffee mixture evenly over the pretzels.
Bake for 5 minutes. Remove the pan from the oven and place on a cooling rack. Immediately sprinkle chocolate chips evenly over the top of the hot caramel and pretzels. Let the chocolate chips sit for 2-3 minutes until they melt. Use an offset spatula or rubber spatula to gently spread the melted chocolate over the top. Lightly sprinkle with sea salt or kosher salt.
Let the it cool completely at room temperature then refrigerate if needed to help the chocolate set up.
Notes
You can replace the pretzels with Saltine or Ritz crackers.