Cut each marshmallow in 6 pieces and toss them in a bowl with the matzo pieces and walnuts.
Put the chocolate in a medium stainless bowl and set it directly in a wide skillet of almost simmering water. Stir until the chocolate is melted and smooth. Remove the bowl from the water and let the chocolate cool, stirring thoroughly and frequently, until it is at 90° F. Pour the matzo mixture over the chocolate and fold until the pieces are thoroughly coated -- there will be just enough chocolate. Use a spoon or your fingers to drop clusters on the parchment paper, or spread all of the mixture in a large layer. Sprinkle very tiny pinches of salt (crushing the largest flakes) over the chocolate.
Refrigerate the pan for 10 to 15 minutes to set the chocolate. Serve at room temperature. Cut the sheet into squares or random pieces with a sharp knife, or break them apart with your hands.
My career was sparked by a single bite of a chocolate truffle, made by my Paris landlady in 1972. I returned home to open this country’s first chocolate bakery and dessert shop, Cocolat, and I am often “blamed” for introducing chocolate truffles to America. Today I am the James Beard Foundation and IACP award-winning author of ten cookbooks, teach a chocolate dessert class on Craftsy.com, and work with some of the world’s best chocolate companies. In 2018, I won the IACP Award for Best Food-Focused Column (this one!).