To begin with, toast slivered almonds in oven (watch carefully--they burn fast!). Set aside. Spread a sheet of parchment paper over clean counter top (about 2 feet long). If necessary, tape down corners.
Using an 8 quart, heavy-weight pot, begin melting butter on high heat. When half of it is melted, add the sugar. Begin stirring to mix, and when small bubbles begin to appear, turn heat town to med-high.
Keep stirring mixture constantly to keep from burning (be alert to a burned odor). When it turns the color of peanut butter, take off heat and add slivered almonds. Stir together quickly, then pour onto parchment paper and spread mixture to about 1/2 inch.
Add broken pieces of chocolate bar over top, and when melted (10-20 seconds later), begin spreading over the roca mixture. Lastly, sprinkle almond slices over top.
Cutting the candy works best after refrigerating slab for half an hour. When chocolate is no longer shiny and wet, put slab back on counter top, and with a large, sharp chef's knife, press down through candy to break into rows. Cut alternate rows until you have little squares.
* You could also push the point of the knife down into candy and break into different uneven-sized shapes.
Package in small to medium sized cellophane bags and keep refrigerated until you hand them out. They're tastier if left to room temperature when serving. This recipe should yield around 8 small cello bags of candy to give out.