1. Place pecans in a single layer on a baking sheet.
2. Bake at 350° for 8 to 10 minutes or until toasted.
3. Line a 17- x 12-inch jelly-roll pan with parchment paper. Break each chocolate bar into 8 equal pieces. (You will have 48 pieces total.) Arrange in a checkerboard pattern in jelly-roll pan, alternating white and dark chocolate. (Pieces will touch.)
4. Bake at 225° for 5 minutes or just until chocolate is melted. Remove pan to a wire rack. Swirl chocolates into a marble pattern using a wooden pick. Sprinkle evenly with toasted pecans and salt.
5. Chill 1 hour or until firm. Break into pieces. Store in an airtight container in refrigerator up to 1 month.
*3/4 tsp. kosher salt may be substituted.
Note: For testing purposes only, we used Ghirardelli 60% Cacao Bittersweet Chocolate Baking Bars and Ghirardelli White Chocolate Baking Bars.