Place vanilla squares, white chocolate squares, and 2 Tbsp. shortening in a microwave-safe bowl. Microwave at HIGH 1 to 2 minutes or until white chocolate is soft; stir until smooth. Dip 18 graham cracker squares entirely in melted white chocolate. Place dipped grahams on a parchment paper-lined baking sheet. Chill 20 minutes or until white chocolate is firm. Repeat procedure with chocolate squares, remaining 2 Tbsp. shortening, and remaining graham crackers. Drizzle any remaining semisweet chocolate and white chocolate over dipped grahams; sprinkle with toffee bits. Chill until firm.