Preheat oven to 350°F (175°C).
In a bowl, mix the flour, cocoa, baking soda, and salt.
Cream the butter with the brown sugar.
Add the eggs and corn syrup to the butter mixture.
Gradually add the dry ingredients.
Mix until the dough is smooth.
Fold in the dark, milk, and white chocolate, and the cashews (optional).
Line a baking sheet with parchment paper.
Scoop out 2 tablespoons of dough and roll into balls.
Place each dough ball on the sheet, spacing them apart.
Top with a few extra white chocolate pieces, if desired.
Bake for about 10 minutes, until the centers are no longer shiny.