Preheat the oven to 375°F. Line a sheet tray with a layer of foil, then cover the foil with a sheet of parchment. Evenly cover the sheet tray with matzos. Break or cut the matzos into smaller pieces if necessary.: The first thing you will notice is the cool metallic scent of the foil and the dry, papery sound of the matzos as you arrange them. Setting a stable, lined tray is essential because the toffee will be very hot and sticky; parchment over foil helps you lift the finished pieces cleanly. Make sure the matzos sit in a single layer with minimal overlap so the toffee can coat each piece evenly. A common mistake is crowding the pan which leads to uneven coating and inconsistent baking. Take a moment now to preheat accurately, because oven temperature affects how quickly the toffee bubbles and browns.
In a heavy bottomed saucepan, combine the butter, brown sugar, and a generous pinch of sea salt. Cook over medium heat, whisking constantly, until the mixture comes to a boil (about 2 to 4 minutes). Boil for 3 additional minutes and continue stirring constantly.: You will see the butter melt and the brown sugar dissolve into a glossy amber syrup, and you should hear a steady gentle bubbling as the mixture reaches a boil. The heavy bottomed saucepan ensures even heat distribution which prevents hot spots that can scorch the sugar. Whisking constantly keeps the texture smooth; if you stop stirring the sugar can stick and crystalize, producing a grainy toffee. A typical error is cranking the heat too high to hurry things along, which risks burning and a bitter flavor. Aim for an even medium heat and steady attention.
Remove from the heat and pour the toffee mixture over the matzos.: When the mixture leaves the pan it will be fluid and glossy, a deep caramel color, and you will smell warm butterscotch notes. Pour in an even stream along the center, allowing the syrup to flow outward so you do not overload one area. The hot toffee will begin to set at the edges quickly, so pour with confidence and speed. If you hesitate too long it will thicken and become harder to spread. Avoid pouring from too high up as that can lead to splashing and uneven coverage.
Use a spatula to spread evenly across the entire surface of the matzo. Make sure you spread it out fairly quickly or it will start to get sticky and become harder to smooth over.: The spatula will glide through the warm syrup at first, leaving a glossy finish; as it cools the surface will lose shine and resist spreading. Use swift, smooth strokes to encourage even coverage so every inch of matzo is coated. The ideal final look is a uniformly thin layer, not puddles. A common slip is overworking the toffee which causes it to thicken and pull; if that happens, heat gently for a few seconds off the heat to loosen it, but do not scald.
Place the baking sheet in the oven and immediately reduce the heat to 350 degrees F. Bake for 15 minutes. Check frequently to be sure that the mixture is not burning. If it appears to be browning too quickly, remove the tray from the oven and reduce the heat to 325 degrees F, then replace the tray when the temperature drops a bit.: In the oven the toffee will bubble and emit a nutty caramel aroma, and the edges may darken slightly as the sugars concentrate. Reducing the oven temperature immediately controls the rate of browning so the surface crisps without developing a burnt note. Keep your eyes on the tray in the last five minutes to catch any early browning. A frequent problem is leaving the oven door closed without checking, which can let the sugars cross from caramelized to scorched in a heartbeat. If you see rapid darkening, intervene early to prevent bitterness.
Once 15 minutes have passed, remove the matzos from the oven and evenly sprinkle the chopped chocolate chips over the top.: The heat from the toffee and the pan will be enough to begin softening the chopped chocolate . As you scatter the chips, you will smell a warm chocolate hint that signals the next step. Distribute them evenly so you have consistent melt across the surface. If you leave large gaps, you will get uneven patches of chocolate. Resist the urge to press the chips into the toffee; letting them melt naturally gives a smoother finish.
Let stand for 5 minutes, then spread the chocolate over the matzo.: After five minutes the chips will be glossy and partially melted, and the surface will look satiny. Use a spatula to coax the softened chocolate into an even layer, working gently so you do not tear the softer toffee beneath. The tactile cue is a soft, yielding surface that spreads like a satin ribbon. An error here is waiting too long, which causes the chips to set in little lumps rather than forming a cohesive sheet. If that happens, warm the sheet briefly in the oven for a few seconds to loosen the chocolate.
Sprinkle the chopped pistachios and a light sprinkle of sea salt over the top of the melted chocolate.: The contrast of green pistachios and flaky sea salt against dark chocolate is both visual and textural. The nuts will stick into the melted chocolate and add a fresh crunch while the salt enhances the chocolate and toffee flavors. Scatter evenly so each piece gets some topping. A typical mistake is over-salting which masks the delicate caramel notes, so start with a light hand and adjust next time if needed.
While the matzos are still warm, break them into smaller squares or pieces.: Breaking while warm often yields cleaner edges because the toffee is slightly pliable, and you will hear a satisfying crack as pieces separate. Use the parchment to lift the whole sheet and gently snap it into segments, or press down with a spatula for controlled breaks. If you wait until everything is fully cold it can shatter unpredictably into uneven shards. Be mindful of the temperature to avoid ragged pieces.
Place in the freezer until the topping has set. Serve straight from the freezer, chilled, or at room temperature (I prefer it chilled!).: Moving the tray to the freezer produces a rapid set, with the chocolate going from glossy to solid and the toffee achieving its crisp snap. You will notice the temperature shift in the air and the faint condensation on the pan edges as it chills. Serving chilled enhances the snap and the contrast of textures, while room temperature brings out softer chocolate notes. A common oversight is leaving it at room temperature too long which can soften the toffee, so store properly if you need a crunchy finish.