Preheat the oven to 350ºF. Line cookie sheets with parchment paper.
Using a stand mixer or an electric hand mixer, cream together the butter and sugars for about 4 minutes. The mixture should be light in color and fluffy. 1 cup salted butter, ¾ cup granulated sugar , ¾ cup brown sugar
Add the eggs and vanilla and mix again for 1 minute. 2 large eggs, 2 teaspoons vanilla extract
Add in the dry ingredients: flour, cocoa, espresso powder, baking soda and salt. Mix for 30 seconds, just until the mixture is combined. On low speed, gently mix in the in the chopped toffee and chopped dark chocolate. 2 ¼ cups all-purpose flour , ⅔ cup unsweetened cocoa powder*, 2 tablespoons espresso powder, ¾ teaspoon baking soda, ¼ teaspoon salt, 8 Heath toffee bars, 1 dark chocolate bar
Use a 2" cookie scoop to drop the batter onto the lined baking sheets. Space the cookie dough balls about 2" apart. Press a few extra toffee pieces on the top of the cookies. Bake the cookies for 10 minutes or until they are set. If you want the cookies to stay soft and chewy, do not over bake. 2 Heath toffee bars
Allow the cookies to cool for 5 minutes on the pan, then remove to a wire rack to cool completely.
Notes
*Remove one tablespoon of regular cocoa powder and replace with one tablespoon of black cocoa powder to get a rich, dark color. (55 grams regular cocoa powder and 10 grams black cocoa powder).
For traditional size cookies, each cookie should be 1.5 ounces of dough. For large Levain style cookies, use 3 ounces of dough per cookie. Refrigerate the cookie dough balls for 30 minutes Then bake for 8 minutes at 425ºF. If they still spread slightly, use a knife to gently push in the edges of the cookie to round them out. You could also add ½ tablespoon cornstarch to the dough which will help the cookies stay thick.
These cookies will not spread much, but if you want them to be extra thick, refrigerate the cookie dough balls for 20-30 minutes. This is not necessary though and in the pictures shown, we did not refrigerate the dough.
Store in an airtight container at room temperature for 3 days or freeze for up to 2 months.