Preheat the oven to 400?F. Line two baking sheets with parchment paper.
In a medium-size sautÈ pan, melt 4 tablespoons of the butter over medium heat. Add the brown sugar and stir until the sugar dissolves and the mixture is bubbly, about 1 minute. Add the pecans, salt, cayenne, nutmeg, and cinnamon and cook, stirring constantly, until the sugar starts to caramelize and coats the pecans evenly, about 3 minutes.
Remove the pan from the heat and spread the pecans over one of the prepared baking sheets. Place the pan in the oven and roast for about 6 minutes. Remove from the oven and, using a fork, place the pecans evenly on the parchment paper. Let cool completely.
Fill three small saucepans halfway with water. Place the pans over medium heat and bring to a simmer, then reduce the heat to medium-low. Put each type of chocolate into a separate stainless steel mixing bowl. Place each bowl over a saucepan and stir until the chocolates are completely melted. Remove from the heat and stir 1 tablespoon of the remaining butter into each bowl until completely melted.
Pour the semisweet chocolate onto the second prepared baking sheet and spread evenly with a rubber spatula. Then pour the milk chocolate over the semisweet layer and spread evenly with a rubber spatula. Repeat with the white chocolate. Sprinkle the pecans and the cherries over the chocolate and press gently but firmly into it. Place the baking sheet in the refrigerator and chill until the bark sets, about 2 hours.
Break the bark into pieces and serve. The bark can be stored between layers of parchment or waxed paper in airtight containers in the refrigerator for up to 2 weeks.
Yield: about 4 pounds