Add butter to a small skillet. Melt over medium heat and cook until bubbly, light to medium brown in color (not too dark) with little bits on the bottom of the pan, approximately 5-6 minutes (making sure not to burn). Cool completely.
In a large mixer bowl, beat cooled brown butter, both sugars and vanilla extract until creamy. Add eggs, one at a time, beating well after each addition.
In a separate bowl, combine flour, espresso powder, baking powder, baking soda, and salt. Gradually add the flour mixture to the wet ingredients (in 2-3 batches to prevent over mixing the flour) until a cookie dough forms, making sure not to over mix. Fold in chocolate, peanut butter cups, caramel, and pretzels. Refrigerate cookie dough for at least 2 hours or preferably overnight (if you have time). Chilling cookie dough will intensify the flavor and color, plus, prevent dough from over spreading.
Preheat oven to 350ºF. Line 3 sheet pans with parchment paper.
With a cookie scoop, portion out ¼ cup cookie dough rounds onto prepared sheet pans. Space 6 cookie balls at an equal distance apart. Bake cookies for 9 minutes, until the cookies are puffed slightly in the center. Carefully lift the sheet pan and gently tap down a couple of times against the oven rack, to flatten them down. Continue baking for 6 minutes, about 15 minutes total. Remove sheet pans from the oven. Cookies will continue baking out of the oven with the residual heat. Cool for 10 minutes; remove to wire rack to cool completely. Sprinkle with flaky salt. Enjoy!
