Preheat your oven to 375°F. Line a 15"x10" cookie sheet with rims with parchment paper.
Lay a single layer of saltine crackers in the pan.
Place the butter and brown sugar in a small saucepan over medium-low heat. Bring to a boil, stirring frequently. As soon as it comes to a full boil, reduce the heat to low and cook for exactly 3 minutes (set a timer!), stirring constantly.
Pour the brown sugar butter mix over the saltine crackers, so that it's evenly distributed.
Transfer to the oven and bake for 5 minutes. It will be very bubbly when you pull it out. Place it on a cooling rack and immediately sprinkle with the chocolate chips.
Wait a couple of minutes for the chocolate chips to begin melting, then use an offset spatula or butter knife to spread the melted chocolate evenly over the saltines and caramel.
If you'd like, you can add Christmas themed sprinkles and/or M&Ms. I love to use mini M&Ms on these. A light layer of flaky sea salt is always good, too!
Let the saltine toffee cool until hard (this may take an hour or more). If you want to accelerate the process you can place it in the fridge to cool.
Cut into squares to serve.