Preheat the oven to 300F for the spiced pecans.
Melt 8 tablespoons butter in a large skillet. Add 1½ cups brown sugar and spices (dry mustard, cayenne pepper, ground cumin), remove from heat and stir to dissolve.
Let the mixture cool, then stir in the egg white.
Pour the mixture over ½ pound pecan halves in a large bowl and stir until evenly coated.
Transfer the pecans to a baking sheet in a single layer and toast in the preheated oven, shaking and tossing 2-3 times, until golden brown, about 20 minutes.
Transfer the pecans to a bowl and rub between your hands when cool enough to handle to distribute sugar coating evenly.
Combine ⅔ cup brown sugar and ⅓ cup water in a heavy-bottomed saucepan and bring to a boil.
Cook over medium heat until the mixture reaches soft ball stage (240F), about 4 minutes from boiling.
Let the mixture cool slightly, then stir in ½ cup heavy cream.
Continue to boil for another 3-4 minutes until glossy and slightly thickened.
Remove from heat and stir in 4 tablespoons butter.
Fold in the spiced pecans.
Cut the top rind evenly off the 8-inch wheel of Brie cheese.
Pour the caramel evenly over the top of the cheese, distributing the pecans with a knife or spoon.
Serve with slices of French bread, crackers or apple wedges.
