Preheat the oven to 350°F. Line an 18 by 13 inch half sheet pan with foil, then arrange the crackers in a single layer, placing them as close together as possible.
In a medium saucepan, mix the butter, brown sugar, vanilla, and salt over medium high heat. Stir until everything melts and comes to a boil. Let it cook for 2 to 3 minutes, stirring now and then, until the mixture starts to foam and thicken slightly. Remove from the heat and quickly pour it over the crackers, spreading it to cover them as evenly as possible.
Place the sheet pan in the oven and bake for 12 to 14 minutes, until the sugar mixture is bubbling and turns a deep golden brown. Remove from the oven and right away scatter the white chocolate chips evenly over the top. Let them sit for about 3 minutes to soften and melt. Use an offset spatula or the back of a spoon to spread the melted white chocolate all the way to the edges, covering the toffee layer. Finish by sprinkling the peppermint candies and sprinkles on top while the chocolate is still warm.
Allow the bark to cool completely before cutting or breaking it into pieces. This will take about 2 hours at room temperature, or around 30 minutes if you place it in the refrigerator.
