1. Spray a 9 x 13-inch baking pan with nonstick cooking spray and set aside.
2. Melt butter in large nonstick saucepan over medium-low heat. Add marshmallows and melt, stirring constantly, until they begin to break down at edges, about 1 1/2 minutes. Add chocolate, cocoa (if using), vanilla, and salt and continue cooking, stirring constantly, until both marshmallows and chocolate melt completely. Blend until uniform, about 2 1/2 minutes longer.
3. Remove from heat and quickly but gently add rice cereal to pan and mix with a sturdy spoon or rubber spatula, trying not to crush cereal, until all cereal morsels are coated with chocolate-marshmallow mixture. Scoop mixture into prepared baking pan and press into an even layer of about 1 inch. Use a metal spoon dipped in water to smooth the surface. Slice into 24 pieces. Tip: Use cookie cutters to make creative shapes rather than cutting into squares.
4. Place white chocolate in a microwave safe bowl and melt in microwave set at 50 percent power, 1 to 2 minutes (alternatively, melt white chocolate in a small metal bowl set over a small saucepan of barely simmering water, stirring occasionally). Stir until chocolate is uniformly melted and smooth. Pour melted chocolate into a small plastic sandwich or zip-close bag and squeeze it into one bottom corner. Snip a tiny hole in that corner with scissors so that chocolate will flow out in a steady, easily controlled stream, and pipe chocolate onto surface of crisped rice treats in any design you choose. Let white chocolate set for at least 30 minutes. Serve treats at room temperature.
Source: Hannaford fresh Magazine, January - February 2007