Preheat oven to 350ºF. Completely line a rimmed baking sheet (approximately 11” x 17") with foil, making sure the foil goes up and over the edges. Put a sheet of parchment paper on top of the foil.
Line the baking sheet with matzoh. You’ll need to cut up some of the pieces to complete the job. Interestingly, although every sheet of matzoh comes perforated, the perforations never, ever help you break the cracker in any remotely linear way. I recommend cutting up the matzoh by laying each board on a smooth, flat surface, taking a serrated bread knife and pressing down with its blade between, not along, the lines of perforations. (Insert heavy sigh here.)
In a 2- or 3-quart heavy saucepan, melt the butter and brown sugar together, over moderate heat, until the butter is completely melted, everything is mixed together, and the mixture is beginning to boil. Stir the mixture constantly, as it simmers, for three minutes. Turn off the heat. Add 1/2 teaspoon sea salt and the vanilla, stir well, and right away pour it over the matzoh. Use a spatula to spread it around evenly.
Put the pan in the oven. Bake for 10 to 12 minutes. Keep an eye on it! It is going to get all bubbly and seething looking. That’s okay. But watch the edges carefully. If they start to darken, take the pan out of the oven for a minute, then return it. You want to bake for about 10 to 12 minutes altogether.
Remove the pan from the oven, turn off the oven, and set the pan on the stove top or counter. Drop the semisweet chocolate chips over half the surface and the white chocolate chips over the other half. Slide the pan back into the warm oven for a minute. Take it out, then using a spatula, spread the melty chocolate chips evenly over the caramel. (Use a different spatula for the white chocolate chips.) Once everything is nice and spread around, immediately scatter the chopped nuts and the remaining tablespoon of sea salt over the entire surface. Then add any other flavorings you may want to use.
Set the baking sheet on a rack and let it cool completely. When the toppings are fairly set, it will help to remove the matzohs carefully from the pan and let them dry on racks.
Once the sheets are completely cool and set, break into pieces. To get perfect linear strips, use a serrated bread knife. Or just break and crack them into strips and chunks. Store in an airtight container in the refrigerator.
We will be serving this stacked on serving plates. Another handsome presentation, when you succeed in cutting this into long strips, is to stand the pieces vertically in glass tumblers.
Theoretically it keeps well for a week. We are unable to confirm this statement.