Line a jelly roll pan with parchment paper and lay out your saltines in a single layer.
Preheat your oven to 325°F.
In a saucepan, melt the butter and brown sugar over medium heat. Bring to a boil and let it bubble for 2–3 minutes, stirring occasionally.
Pour that butter over the crackers and quickly spread it out evenly with a spatula.
Pop the tray into the oven for 6–8 minutes.
Remove from the oven and immediately sprinkle the white chocolate chips on top.
Let them sit for a minute or two to soften, then spread the melted chocolate over the toffee layer.
Sprinkle on the M&Ms and festive sprinkles while the chocolate is still melty.
Let the candy cool, then chill in the fridge for about 1 hour to set.
Once set, break into pieces.