Directions:

12 ounces high-quality dark chocolate, such as Guittard or Valrhona, 60-72% cacao
1 cup (2 sticks) unsalted butter, cut into 1-inch slices
1 teaspoon kosher salt or ½ teaspoon table salt
1 tablespoon vanilla extract
5 large eggs
¾ cup packed dark brown sugar
1 cup granulated sugar
1¼ cups all purpose flour

Preheat oven to 350 degrees F and place an oven rack in the middle position of the oven. Line a 9-by-13-inch metal baking pan with parchment paper, leaving some extra around the edges so the brownies can be easily lifted from the pan. Spray lightly with cooking or baking spray.

If using dark chocolate bars (as opposed to baking wafers or chocolate chips), chop ⅔ of the chocolate finely using a serrated knife and place in a large, heatproof bowl. Chop the remaining ⅓ of the chocolate into ½-inch chunks; set the chunks aside in a small bowl. Add butter to the chocolate in a heatproof bowl.

To melt chocolate using a double boiler: Add 2 inches of water to a saucepan and bring it to a simmer over high heat. Reduce heat to low and place heatproof bowl on top. (Make sure bottom of bowl doesn’t touch simmering water so the chocolate doesn't "burn" or become grainy instead of smooth.) Stir occasionally with a rubber spatula until chocolate is melted.

Alternatively, to melt chocolate in a microwave: Place heatproof bowl in microwave and microwave at 30-second intervals. Once chocolate starts to melt on bottom and sides of bowl, use a rubber spatula to mix it. When mostly melted, stop microwaving and stir until chocolate melts completely.

Once chocolate is melted, stir in salt and vanilla.

In a large bowl, combine eggs and both sugars. Whisk vigorously until combined well. While whisking, drizzle melted chocolate into the mixture and continue whisking until combined. Sift in flour, and whisk until just combined. Stir in reserved chocolate pieces.

Pour brownie batter into prepared pan and bake until a toothpick inserted into the center comes out mostly clean, except for some melted chocolate - about 30-35 minutes.

Remove the brownies from oven and place on a cooling rack until cool enough to handle, at least 15 minutes.

Lift brownies out of pan with parchment paper and cut into squares before serving.