Cover both sheet pans with aluminum foil.
Cut a piece of parchment paper to fit the bottom of each pan and place it on top of the foil.
Line the bottom of each sheet pan evenly with matzo, breaking extra pieces, as required, to fit any spaces.
In a 3-quart saucepan, or double boiler, combine butter and brown sugar.
Cook over medium heat, stirring constantly, until the mixture comes to a boil (about 2 to 4 minutes).
Boil for 3 minutes—use a timer, this is important—stirring constantly.
Remove from heat, and pour over the matzo, covering completely.
Place the baking sheets in a preheated 375-degree oven and immediately reduce the heat to 350 degrees.
Bake for 15 minutes, checking every few minutes to make sure the mixture is not burning (if it seems to be browning too quickly, remove the pan from the oven, lower the heat to 325 degrees and replace the pan).
Remove pans from the oven and sprinkle immediately with the dark chopped chocolate or chips.
Let stand five minutes, then spread the melted chocolate over the matzo with an offset spatula or knife.
Sprinkle the chopped nuts of your choice on top.
While still warm, break into squares or odd shapes.
Place pans in freezer to chill until set.
Remove and store in an airtight container for up to a week.