Dream Bars

Invert a baking sheet, and spray with cooking spray. Line top with parchment paper. With an offset spatula, spread melted chocolate evenly across parchment. Place baking sheet in the freezer until firm, about 30 minutes.

Lightly coat a quarter sheet or 13x9-inch pan or glass baking dish with cooking spray, and line with parchment paper, leaving 1 inch of overhang on long sides.

In the bowl of a stand mixer fitted with the paddle attachment, beat butter at medium speed for 5 to 10 seconds. Add granulated sugar, and beat until mixture is aerated, 3 to 4 minutes. Scrape sides and bottom of bowl with a rubber spatula to bring batter together.

Add 1 tablespoon water and vanilla to egg yolks. Add egg yolks to butter mixture, one at a time, beating until batter resembles cottage cheese, about 5 seconds per yolk. Scrape sides and bottom of bowl with a rubber spatula to bring batter together. Beat at medium speed for 20 to 30 seconds to make nearly homogeneous.

In a medium bowl, whisk together flour, baking soda, baking powder, and salt.

Add flour mixture to butter mixture, and beat at low speed until dough just comes together but still looks shaggy, about 30 seconds. Do not overmix. Remove bowl from stand mixer. With a plastic bench scraper, bring dough completely together by hand.

Transfer dough to prepared pan. Using a rubber spatula and then your fingertips, press dough into corners of the pan, and smooth the surface. Remove chocolate from the freezer, and break it up into shards. Scatter chocolate shards across the surface of the dough, and then press into the dough. Cover with plastic wrap, pressing down through the plastic to smooth down the top. (You can also use a pastry roller to even out the surface.) Refrigerate until dough is set, at least 20 minutes or overnight. (If refrigerating dough overnight, refrigerate the egg whites as well, letting them come to room temperature before proceeding with the meringue.)

Preheat oven to 350°.

In the bowl of a stand mixer fitted with the whisk attachment, beat egg whites and a pinch of kosher salt at medium speed until frothy, about 45 seconds. Add brown sugar, and beat at medium-high speed until shiny peaks form and the meringue holds its shape, 2 to 3 minutes. Spread meringue evenly over chilled dough.

Bake until meringue resembles a lightly toasted marshmallow, 23 to 25 minutes, rotating pan halfway through baking. It will start to crack on the sides but should still be slightly soft in the center, and the shortbread should be cooked through but still pale—not golden brown. (Do not overbake, or the shortbread will be too crumbly to cut.) Let cool completely in pan. Once cool, refrigerate until chilled.

Using parchment as handles, lift bars out of pan, and transfer to a cutting board. Cut bars lengthwise into 3 strips. Cut bars crosswise into 10 strips to make small, rectangular bars. Serve bars at room temperature. Bars can be refrigerated in an airtight container for up to 5 days.