Preheat the oven to 350 degrees.
Line a baking sheet with parchment paper and spread the 3 cups of whole pretzels over to cover the pan evenly.
Add the butter and brown sugar to a sauce pan and bring the mixture to a boil.
Boil the butter and brown sugar for 2 - 3 minutes, stirring constantly, until thick.
Pour the toffee over the top of the pretzels and use a rubber spatula to spread it out evenly.
Place the pan in the oven and bake it at 350 degrees for 4 - 5 minutes, until the edges are bubbly and browned.
Remove the pan from the oven and immediately sprinkle on the whole bag of chocolate chips evenly over the top of the pretzels.
Allow the chocolate chips to sit for 5 minutes and melt, then use a rubber spoon or spatula to spread the chocolate out to cover the pretzels in an even layer.
Sprinkle the crushed pretzels on top of the melted chocolate.
Place the pan in the fridge or freezer until set, around an hour or two.
Once hardened, use your hands to break the Christmas crack into pieces.
Store leftovers in an airtight bag in the freezer until ready to eat.