Steps:

• Combine the butter and chopped chocolate in a heatproof bowl and set over a saucepan filled with a few inches of simmering water over low heat. Let melt, 3 to 4 minutes, then stir until smooth. Remove the bowl from the pan and let cool slightly. 
• Combine the flour, cocoa powder, baking powder, baking soda and salt in a medium bowl and whisk to combine and get rid of any lumps.
• Combine the brown sugar, eggs, vanilla and ½ cup granulated sugar in a large bowl and beat with a mixer on medium-high speed until light and smooth, 2 to 3 minutes. Add the melted chocolate mixture and beat until combined. With the mixer on low speed, add the flour mixture and beat until just combined, 30 seconds to 1 minute. Cover the dough and refrigerate until firm, at least 2 hours and up to 4 hours.
• Preheat the oven to 350˚. Line 2 baking sheets with parchment paper. Spread the remaining 1 cup granulated sugar in a shallow bowl and the powdered sugar in a second shallow bowl. Scoop the dough into balls (about 1 tablespoon each). Roll first in the granulated sugar, then in the powdered sugar to coat completely. Place on the baking sheet, about 2 inches apart. Bake until the tops of the cookies are cracked and the edges are firm, 10 to 12 minutes. Let cool 5 minutes on the baking sheets, then remove to racks to cool completely.

Steps:

• You can use regular melted butter or browned butter for this chocolate chip cookie recipe.
• For regular melted butter, melt the butter in the microwave or on the stove, and then cool. When cool to the touch, use the melted butter in the recipe below.
• For browned butter (our favorite), melt the butter in a light-colored skillet over medium heat. Swirl the pan occasionally to be sure the butter is melting evenly. As it melts, the butter will begin to foam and the color will change from light yellow to golden, and finally to brown. This only takes a minute or two.
• When the browned butter smells nutty and the butter is a light golden brown, transfer the browned butter to a heatproof bowl to cool. When cool to the touch, use the browned butter in the recipe below.
• In a medium bowl, whisk the flour, baking soda, and salt together. Set aside.
• In a large bowl, whisk the sugars, whole egg, egg yolk, vanilla, and the melted butter or browned butter together. Whisk in espresso powder (optional).
• Switch to a large rubber spatula, and then add the dry ingredients in 3 parts, stirring gently until they disappear. Fold in most of the chocolate chips, saving a handful for adding to the tops of each scooped cookie before baking.
• Heat oven to 325 degrees Fahrenheit (160C) and line a cookie sheet with parchment paper or a silicone baking mat.
• Drop 1 1/2 tablespoon-mounds or use a medium cookie scoop onto baking sheets. Leave 2 inches between the cookies to allow for spreading. (For larger cookies, use 3 to 4 tablespoons of dough and space them apart by 3 inches.) Press a few extra pieces of chocolate into the tops of each cookie dough mound.
• Bake the cookies, one sheet at a time and rotate once during cooking, for 12 to 16 minutes. The cookies should be golden brown around the edges but light in the middles. Let the cookies cool on the baking sheet for 5 minutes then transfer to a wire rack to cool completely. Before serving, sprinkle a few flakes of sea salt over each cookie (optional).
• Store the baked cookies in an airtight container for up to 3 days at room temperature or up to a week in the refrigerator.