Line the baking sheet with parchment paper. Line up the saltine crackers in an even layer. If you are using a larger pan, you can use additional saltines to fill your pan.
In a medium saucepan over low to medium heat, melt the butter.
Once the butter is melted add the brown sugar and bring the mixture to a boil. Boil 2 to 3 minutes, stirring so it doesn’t burn.
Remove the pan from the heat and pour the butter and sugar mixture over the crackers and smooth evenly.
Immediately put the pan into the oven and back for 6 to 8 minutes. You want the brown sugar mixture to be bubbly.
Take the pan out of the oven and immediately sprinkle the white chocolate chips over the top of the crackers so they will melt. Let the crackers sit for 1 to 2 minutes for the chocolate to melt and then smooth out evenly over the top with a silicone spatula.
Sprinkle the M&Ms and sprinkles over the melted chocolate.
Let the bark cool and then move the pan to the refrigerator to chill for 1 hour.
Once the cracker bark has cooled and hardened, remove it from the pan and break it into pieces and enjoy.