Preheat oven to 400 degrees. Melt Butter and add brown sugar and stir constantly for several minutes. Stir constantly until the constancy turns foamy and marshmellow like. Pour over saltines making sure the entire pan surface is covered. Place in over for 8 minutes. Remove and sprinkle with both flavors of chips. Wait momentarily for them to soften and then smooth out with the back of a spoon. Run a fork through to mimic the look of tree bark and sprinkle with topping of choice: toffee, PB chips, peppermint, candy bars, etc. let sit for 5 minutes and then place in freezer for one hour.