Preheat the oven to 350°F.

Put the hazelnuts on a large rimmed baking sheet and toast longer than you think you should, until the hazelnuts get pretty dark under their skins and the skin appears to flake off the hazelnuts a bit, about 15 minutes.

Transfer the hazelnuts to a large kitchen towel or, better yet, any sort of a laundered soft cloth bag with a drawstring. Rub the fabric against the hazelnuts until as many of the skins come off as possible. (Of course if you can find preblanched hazelnuts, which I’ve found virtually impossible, you’re ahead of the game here.)

Line the bottom and sides of a large (12- x 17-inch) baking sheet with aluminum foil. Arrange the matzas on the sheet, using a serrated knife to gently saw off parts of each board so they fit into as uniform and flush a single layer as you can. (If you don’t feel like being a geek like me, just snap the matzas and be kind to yourself about the inevitably shattered matzas.)

In a 3-quart saucepan bring the butter and brown sugar to a boil over medium-low heat, stirring, then cook, lowering the flame if the boiling gets out of control, until a smooth caramel forms, 3 minutes. Quickly pour the bubbling caramel over the matzo, smooth it out a little with an offset spatula, and bake it until browned and the edges burn slightly, 17-18 minutes (I’m purposely going for this slightly burnt thing, but if you’re not, take it out at 15 minutes). Some of the caramel may have slipped under the matzas; this is cool, too.

Remove from the oven, sprinkle the chocolate on top and return to the oven for 30 seconds to help it melt. Remove it from the oven and let the chocolate melt a little more on the counter, 1-2 minutes. Using that offset spatula again, spread the chocolate evenly all over, cool for a minute, sprinkle the surface of the chocolate with the salt, then sprinkle with the hazelnuts. Chill, uncovered, until solid, 40-45 minutes, then break with your hands or cut into even and symmetrical slices with the serrated knife. The finished product will keep in the fridge in an airtight container for a couple of weeks (as if).