Preheat the oven to 375, and ensure a rack is in the center position in the oven. Line a light-metal cookie sheet with a silicone mat. This creates the best cookies that don’t spread too much, yet still have crackles, chewy centers and crisp edges. Dark pans make crisper cookies that cook much faster, and the lack of a silicone mat causes cookies to spread too much, typically.

In a medium bowl, add the butter and brown sugar. Beat with an electric mixture on medium speed until light and fluffy at least one full minutes. Creaming the butter and sugar together very well helps create beautiful cracks on the cookies.

Next, add the egg yolk and vanilla extract, and beat to combine.

Finally, sprinkle the flour, salt, baking powder, and baking soda evenly over the top of the butter mixture. Beat the flour mixture into the butter mixture using the electric mixer until everything is combined.

Stir in the chocolate chips and chopped chocolate.

Scoop out 10 balls of dough, and space them evenly on the cookie sheet. You can roll them in your hands to create perfect balls that will make perfectly round cookies, if you prefer.

Bake for 9-10 minutes. When the edges of the cookies are just starting to brown, remove the cookies from the oven. When they first come out, they will appear puffy. As they cool, they will flatten and create a crackly surface with a chewy center.

Let cool on the baking sheet for 5 minutes to set up, and then move to a wire rack to cool completely before serving.