Preheat oven to 400°F and line a baking sheet with parchment paper or nonstick foil; spray thoroughly with cooking spray.
Evenly spread pretzels over the prepared baking sheet and set aside.
In a medium saucepan, melt butter and brown sugar over medium heat, stirring continuously until bubbling; simmer gently for 1 minute to thicken caramel.
Pour the caramel sauce evenly over the pretzels on the baking sheet.
Bake in the oven for approximately 7 minutes, optionally rotating the pan midway.
Remove the baking sheet and immediately sprinkle chocolate chips over the caramel; spread evenly with a spatula to cover all pretzels.
If the chocolate chips do not melt easily, return the sheet to the oven for 1-2 minutes, then spread again.
Sprinkle M&M's and Christmas sprinkles over the melted chocolate before it sets.
If desired, melt almond bark in two bowls, tint one with red and the other with green food coloring, then drizzle over the bark using spoons or piping bags.
Allow the bark to cool completely at room temperature until set, about 1 hour.
Break the bark into pieces or slice carefully with a sharp knife for serving.