An ode to my favorite baked good of all time, the fudgy brownie, this cookie has a healthy salt content and, to me, is perfection. I freeze a few of these in the dense heat of a New York summer for my lunch or afternoon snack.
*Note: You can substitute 2 tablespoons corn syrup for every ¼ cup glucose.
Preheat the oven to 300 degrees.
Combine the flour, cornstarch, sugar, cocoa powder, and salt in the bowl of a stand mixer fitted with the paddle attachment and paddle on low speed until mixed.
Add the butter and paddle on low speed until the mixture starts to come together in small clusters.
Line a sheet pan with parchment paper or a Silpat. Spread the clusters on the pan, and bake for 20 minutes, breaking them up occasionally. The crumbs should still be slightly moist to the touch at that point; they will dry and harden as they cool.
Let the crumbs cool completely before using in a recipe or eating. Stored in an airtight container, they will keep fresh for 1 week at room temperature or 1 month in the refrigerator or freezer.
Combine the butter, sugar, and glucose in the bowl of a stand mixer fitted with the paddle attachment and cream together on medium-high for 2-3 minutes. Scrape down the sides of the bowl, add the egg, vanilla, and melted chocolate, and beat for 7-8 minutes.
Reduce the mixer speed to low and add the flour, cocoa powder, baking powder, baking soda, and salt. Mix just until the dough comes together, no longer than 1 minute. (Do not walk away from the machine during this step, or you will risk overmixing the dough.) Scrape down the sides of the bowl with a spatula. Still on low speed, add the chocolate crumbs and mix just until incorporated, about 30 seconds.
Line a sheet pan with parchment paper. Using a 2 ¾-ounce ice cream scoop (or a 1/3-cup measure), portion out the dough onto the pan. Pat the tops of the cookie dough domes flat. Wrap the sheet pan tightly in plastic wrap and refrigerate for at least 1 hour, or up to 1 week. Do not bake your cookies from room temperature — they will not bake properly.
Preheat the oven to 375 degrees. Line a sheet pan with parchment paper or a Silpat.
Arrange the chilled dough a minimum of 4 inches apart on the sheet pans. Bake for 18 minutes. The cookies will puff, crackle, and spread. It's tough (kind of impossible) to gauge if a cookie that is this dark with chocolate is done. If after 18 minutes, the cookies still seem doughy in the center, give them another minute in the oven, but not more.
Cool the cookies completely on the sheet pans before transferring to a plate or an airtight container for storage. At room temperature, the cookies will keep fresh for 5 days; in the freezer, they will keep for 1 month.