1 1/2 cups (3 sticks) unsalted butter
Flaky sea salt, such as Maldon
6 sheets matzo (the thin, crispy salted sort are nice if you can find them)
1 1/2 cups packed dark-brown sugar
1 teaspoon vanilla extract
1/2 teaspoon kosher salt
12 ounces (2 cups) semi-sweet or bittersweet chocolate chips
1 cup chopped pecans, toasted
1. Organize: Melt butter in a large saucepan. Brush a little of the butter onto a large (22 x 15) rimmed baking sheet. Fit with parchment paper, allowing for some overhang. Brush parchment lightly with butter. Sprinkle lightly with flaky salt. Line up matzos on buttered parchment, touching, but not overlapping (if you have to crack off a couple edges to make it all fit neatly, do what you must). Heat oven to 400 degrees.
2. Thicken: Whisk brown sugar and vanilla into remaining butter. Set over medium-high heat. Bring to a boil; boil until thick and 245 degrees, about 2 - 3 minutes. Pour evenly over matzos.
3. Bake: Slide pan into oven and bake until light brown and bubbly (and not over 245 degrees), about 3 minutes. Carefully pull pan out of oven.
4. Gild: Scatter molten surface with chocolate chips. Let melt, 5 minutes. Use an offset spatula to spread chocolate. Cast on nuts; gently press into chocolate. Scatter lightly with flaky sea salt.
5. Cool: Let rest at room temperature until set, or, if you're having trouble waiting, freeze firm, 30 minutes.
6. Cut: Lift parchment by its overhang, and set toffee (paper and all) on a cutting surface. Slice into matzo-sized squares. Wrap each in foil, return to matzo box and bring along to your seder as a hostess gift.