Place pecans in a single layer on a baking sheet. Bake until toasted, 8-10 minutes.
Decrease oven temperature to 225 degrees.
Line a 17" x 12" jelly roll pan with parchment paper. Break each chocolate bar into 8 equal pieces. You will have 48 pieces total. Arrange in a checkboard pattern in jelly roll pan, alternating white and dark chocolate. Pieces will touch each other like puzzle pieces.
Bake chocolate for 5 minutes or just until melted. Remove pan to a wire rack. Swirl chocolates into a marble pattern using a wooden pick. Sprinkle chocolate evenly with toasted pecans and salt.
Chill 1 hour or until firm. Break chocolate into pieces. Store in an airtight container in refrigerator for up to one month.