Preheat the oven to 350F.
Place the butter and brown sugar in a medium-sized saucepan over medium heat and melt.
Avoid the urge to stir it too much, as that can separate the caramel.
Meanwhile, line a baking tray and cover the bottom with saltine crackers (or Ritz crackers - my favourite!)
Bring the caramel to 250F if you have a candy thermometer, or to about this colour - it should be a consistent texture with no standing butter.
Pour the caramel over the crackers and spread to the edges with an offset spatula.
Place the tray in the oven for 5 minutes until the caramel has formed a hard candy with the crackers.
Sprinkle enough white candy melts or chocolate chips over the toffee to cover it completely, and then melt in the microwave in 30-45 second bursts. Spread with an offset spatula to cover.
Place the peppermint candies in a small bag and smash with a mallet or rolling pin.
Sprinkle the crushed peppermints over the melted chocolate while it is still wet and then add on sprinkles, if using.
Place the whole thing in the fridge and allow to set at least one hour.