- 1 cup (2 sticks) unsalted butter, room temperature, plus more for dish
- 1/2 cup (packed) light brown sugar
- 1/2 teaspoon fine sea salt
- 1 1/2 teaspoons vanilla extract
- 1 1/2 cups all-purpose flour
- 6 ounces semisweet or bittersweet chocolate or high-quality milk chocolate, finely chopped
- 1-1 1/2 cups assorted toppings, such as cocoa nibs, crushed candy, toasted chopped almonds and pistachios, lightly toasted coconut, and popcorn
- Flaky sea salt (such as Maldon)
Arrange a rack in middle of oven; preheat to 375°. Line the bottom and sides of a 13x9x2 inches metal or glass baking dish with foil, allowing 2 inches overhang on either side; butter foil in dish.
Using an electric mixer at medium speed, beat 1 cup butter in a large bowl until smooth, about 3 minutes. Add both sugars and salt; continue to beat until mixture is light and creamy, about 3 minutes longer. Beat in vanilla, then slowly mix in flour, beating until entirely incorporated (dough will be wet and sticky).
Scrape dough into prepared dish. Using your fingertips, spread into a thin, even layer.
Bake cookie base until it is golden brown and has begun to puff and crack, about 22 minutes. DO AHEAD: Base can be made 2 days ahead. Let cool completely and store airtight at room temperature.
Preheat oven to 375°. Scatter chopped chocolate evenly over cookie base and bake just until chocolate is soft and has begun to melt, about 2 minutes. Immediately spread chocolate in an even layer over base.
Scatter toppings over warm chocolate; lightly but firmly press into chocolate. Sprinkle with salt. Let cool in dish on a wire rack for 15 minutes. Using foil overhang, lift cookie from dish. Place on rack; let cool until chocolate is set, about 2 hours.
Carefully remove foil from cookie and slide onto a cutting board. Cut into bars. DO AHEAD: Crunch Bars can be made 5 days ahead. Store airtight at room temperature.