Preheat the oven to 350°. In a microwave safe bowl add chopped chocolate and melted butter. Heat for 30 seconds at a time, mixing in between each, until melted and smooth. Set aside to cool.
In the bowl of a stand mixer beat together the eggs granulated and brown sugar, and vanilla, until the mixture is light and combined, about 3 minutes. Pour in the melted chocolate and stir to combine.
Add in corn starch, baking powder, flour, salt and cocoa powder and mix until just combined. Use a spatula to fold in the chocolate chips and toffee bits. Refrigerate for 30 minutes. Use a cookie scoop to make 24 even dough balls. Line a baking sheet with parchment paper and place cookie dough about 2 inches apart. These cookies will spread a bit so make sure there is enough room in between! Bake for 10minutes or until the edges are just set.
Remove from the oven and immediately use a round cookie cutter or utensil to reshape the cookies (see the blog post above for a detailed description on how to do this). Allow to cool completely on the cookie sheet before transferring to a cookie rack!