Begin by preheating your oven to 350°F (175°C). In a microwave-safe bowl, combine the 8 ounces of bittersweet chocolate and 4 tablespoons of unsalted butter. Microwave in 30-second intervals, stirring after each, until melted and smooth. Be cautious not to overheat; let it cool slightly.
In a large mixing bowl, whisk together the granulated sugar and the melted chocolate mixture until well combined. Then, add the 3 large eggs, 1 teaspoon of instant coffee, and 1 teaspoon of vanilla. Mix until everything is well blended and smooth.
In another bowl, whisk together the all-purpose flour, cocoa powder, baking powder, and salt. This will ensure even distribution of the baking powder and salt within the flour.
Gradually add the dry mixture to the wet mixture, stirring gently with a rubber spatula. Be careful not to overmix; just fold until you see no more flour streaks.
Gently fold in the 8 ounces of toffee bits until they are evenly distributed throughout the cookie dough.
Using a cookie scoop or tablespoon, drop rounded tablespoons of dough onto a baking sheet lined with parchment paper, leaving space between each cookie for spreading. Bake in the preheated oven for 10-12 minutes, or until the edges are set but the centers are still soft.
Once baked, allow the cookies to cool on the baking sheet for about 5 minutes before transferring them to a cooling rack. Enjoy these Toffee Brownie Cookies warm or at room temperature!