Preheat oven to 400 degrees F. Line a rimmed 13-by-9-inch baking pan with nonstick foil or spray with cooking spray. Arrange the saltines, salt side down, in a single layer in the pan. Set aside.
Melt 1 cup butter in a large heavy-duty saucepan over medium. Add the brown sugar and cayenne pepper and raise temperature to high to bring to a boil. Cook for 3 minutes. Immediately pour toffee mixture over the saltines and bake for 6 minutes.
Remove from oven and nudge the saltines back together if they're floating in the toffee.Set aside for 3 or 4 minutes.
Melt the chocolate over medium heat in the top of a double boiler set over a pan of simmering water. (Or place the chocolate in a microwavable container and melt on low power until smooth, about 3 minutes, stirring every 30 seconds.)
Add the remaining tablespoon of butter and the black pepper to the melted chocolate. Pour over the toffee and spread in an even layer with an offset spatula. Top with pecans and dried cherries. Let stand to cool slightly, then sprinkle with sea salt. Transfer to the refrigerator to harden completely, about 1 hour.
Pop loose from the pan, break into pieces, and store in an airtight container separated with sheets of waxed paper or parchment paper.