Preheat your oven to 400°F (200°C). Line a rimmed baking sheet with parchment paper and arrange saltine crackers in a single layer, edges touching.
In a medium saucepan over medium heat, melt the butter. Stir in brown sugar and bring to a gentle boil—let it bubble for 2–3 minutes while stirring constantly.
Carefully pour the hot toffee sauce over the crackers, spreading evenly with a spatula so each square is coated.
Bake for 5–7 minutes, or until the toffee is bubbling and lightly golden at the edges.
Remove from the oven and immediately sprinkle chocolate chips evenly over the hot toffee and crackers.
Let the chips sit for 1–2 minutes to soften, then spread the melted chocolate into a smooth layer with an offset spatula.
Optional: Sprinkle chopped nuts or festive sprinkles on top, gently pressing them into the chocolate.
Allow the bark to cool completely at room temperature or pop it in the fridge for 15–20 minutes until set.
Break the bark into pieces and serve—or package in cellophane bags for gifting!