Brown the butter in a saucepan over medium heat, watching carefully until the milk solids turn golden brown and the butter smells nutty. Transfer to a mixing bowl, including the browned bits.
Stir in ground espresso or coffee and allow to cool at least 30 minutes.
In a medium bowl, whisk together the flour, baking soda and salt. Set aside.
In a large bowl, combine the cooled browned butter, brown sugar, and granulated sugar. Mix until well incorporated.
Add the egg, egg yolk and vanilla extract or paste. Mix until combined.
Add the dry ingredients and mix just until incorporated.
Roughly chop the dark chocolate and reserve a few pieces for topping the cookies.
Fold in the chopped dark chocolate
Portion the dough onto a baking sheet, leaving space between the cookies for spreading. Add the reserved chocolate chunks to the tops.
Bake at 350°F for 8–10 minutes, or until the edges are set and the centers remain slightly soft.
Remove the baking sheet from the oven and carefully tap it gently against a sturdy, heat-safe counter to create ripples around the cookie edges.
While the cookies are still warm, use a round cookie cutter slightly larger than each cookie to gently scoot the edges into a round shape.
Let the cookies cool on the baking sheet for a few minutes, then transfer them to a cooling rack.
