Step 1Heat the oven to 350 degrees. Stack 2 jellyroll pans together and line them with foil, then with a sheet of parchment paper.
Step 2Line the jellyroll pan with matzos as evenly as possible, cutting them into pieces to fill in any gaps.
Step 3Heat the butter and brown sugar in a heavy-bottomed saucepan and bring to a medium boil for 2 to 4 minutes. Remove the mixture from the stove and pour it over the matzos.
Step 4Put the jellyroll pan in the oven and bake for about 15 minutes. Remove the pan from the oven and sprinkle the chocolate over the matzos. Let stand 5 minutes, then smear the top with a metal spatula to spread the chocolate. Garnish the buttercrunch with toasted slivered almonds if desired. Freeze until firm, an hour or less. Break the buttercrunch into pieces, squares or odd shapes to serve.