Preheat oven to 350 degrees. Line baking sheets with a baking mat or parchment paper, set aside.
In a microwave safe bowl, melt one stick of butter (about 45 seconds on HIGH).
In the bowl of a stand mixer or a large mixing bowl, combine the melted/room temperature butter, sugar, and vanilla, beat until light and fluffy (about 2 minutes). Add the eggs one at a time, mix just until incorporated.
In a medium size mixing bowl, whisk together the flour, cocoa powder, baking soda, and salt. With mixing speed on low, gradually add the dry ingredients, adding the dissolved espresso mixture. Mix just until combined. Using a spatula, fold in the chocolate.
Using a standard size cookie scoop (1.5 tablespoons) place dough onto the prepared baking sheets (12 per sheet). Place into the oven and bake for 8-10 minutes. They will look slightly underbaked, but they will firm up and flatten as the cool. Allow them to cool on the sheets for 3 minutes before transferring to a wire rack to cool completely.
Notes
*I've used both unsweetened natural cocoa powder and cocoa rouge, they both yield great results! **You can swap out the white chocolate for milk chocolate chips, peanut butter chips, mint chips, chopped nuts or dried fruit!