Preheat oven to 350° F. Cream the softened butter and brown sugar: Cream together using either a stand mixer or a hand mixer.
Blend in the rest of the ingredients: Add in the flour, chocolate chips, Instant coffee, baking powder, salt, vanilla extract (and optional espresso powder if you have it!) Mix until combined on medium speed.
Press into a 9x13 inch oven safe baking dish: Use clean hands to press mixture down. Or if you feel weird using your hands use the back of a measuring cup or a rubber spatula to press down in an even layer.
Bake for 20 minutes.
Meanwhile, make the top layer: In a small sauce pan over low heat, heat the condensed milk and the butter. Stir occasionally and heat on low until the condensed milk becomes nice and smooth, ~10 minutes. (Keep on low so it doesn't burn the bottom). Remove from heat and stir in the vanilla extract.
Once the cookie layer is done, pour the condensed milk on top in an even layer. Place back in oven and bake again for 10 minutes.
Remove from the oven, it will be bubbling, and sprinkle with sea salt flakes. Let cool for about 30 minutes - 1 hour (if you can wait!). Cut into bars and enjoy. Store in the fridge or freezer. We love these even more day 2 and 3...and 4, so they can easily be made in advance if needed.