Melt butter on low heat. Add marshmallows and stir until melted. Remove from heat.
With the steel knife in your food processor, chop nuts with quick on/off turns, until finely chopped. Add Half the nuts to the marshmallows. Reserve remaining nuts for garnish. Stir in matzo farfel and cinnamon. Mix well. Spread evenly in a buttered 9" x 13" pan. Wet hands and pat down evenly.
Melt chocolate. (I do this in Microwave- 2 minutes on High for 1 lb.). Drizzle over farfel mixture. Sprinkle with reserved nuts. Cool until chocolate is set. Cut into squares.