Preheat your oven to 360 degrees and line a cookie sheet with parchment paper. I used two cookie sheets. Set aside.
If you haven’t already, chop up the chocolate bar into small chunks. They will be used to top the cookie dough balls to get the nice puddles of chocolate. Set aside
In the bowl of an electric mixer fitted with the paddle attachment, cream the cubed butter and both sugars on medium high speed until smooth and creamy, about 4 minutes. With a rubber spatula, scrape down the sides of the bowl. (This step is very important because it helps hold the shape of the cookie. Under mixing will result in a flat and spread cookie.)
On medium speed, add the egg and egg yolk, one at time, and beat for about 30 seconds after each addition. Scrape down the sides of the bowl. Add the vanilla and mix until combined.
With the mixer on the lowest speed, add the flour, baking soda, espresso powder, baking powder, chocolate chips, toffee bits, and salt. Mix just until corporate. Do not over mix, that causes a dry cookie.
Using a large cookie scoop, scoop balls of the dough and then roll the top of the cookie dough ball in the other half of the chopped chocolate and extra toffee piece and place 8 balls onto the prepped pan.
Bake for 12 minutes. The tops and sides will start to brown just slightly, that’s when they are done. Let them sit for 5 minutes before transferring them to a cookie rack to finish cooling.