Preheat Oven: Preheat your oven to 325°F.
Prepare the Pan: Line a 15 x 10 sheet pan with aluminum foil or parchment paper, then grease it lightly with butter or cooking spray. This makes for easy cleanup!
Lay the Crackers: Arrange the saltine crackers in a single layer across the bottom of the pan. Break any crackers as needed to cover the entire surface.
Make the Toffee: In a medium saucepan over medium-low heat, combine the butter and brown sugar. Stir constantly, bringing the mixture to a rolling boil. Let it boil for exactly 3 minutes (or until it reaches about 280°F).
Pour the Toffee: Remove the saucepan from the heat. Immediately pour the toffee mixture evenly over the crackers, using a spatula to quickly spread the toffee across the crackers.
Bake: Place the pan in the oven and bake for 8 minutes. The caramel should be bubbling around the edges when it’s done.
Add Chocolate: After baking, remove the pan from the oven and sprinkle the chocolate chips over the hot caramel. Let them sit for 5 minutes to melt.
Spread and Top: Once melted, use a spatula to spread the chocolate evenly over the caramel layer. Then, sprinkle the M&M's (or chopped nuts) over the top for a festive touch.
Freeze: Place the pan in the freezer for about 15 minutes, or until the chocolate is fully hardened.
Break and Enjoy: Allow the Christmas Crack to sit at room temperature for about 15 minutes. Flip the pan over onto a cutting board and peel off the foil or parchment. Break the candy into pieces.