Preheat the oven to 350° F. Cream the softened butter and brown sugar using either a stand mixer or a hand mixer until light and fluffy, 2-3 minutes.
1 cup softened butter, unsalted (2 sticks, 16 Tbsp.), 1 cup dark brown sugar, packed
Add in the rest of the ingredients: 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. Mixture may seem crumbly, but should come together when you press it between your fingertips.
2 cups all purpose flour, spooned and leveled, 1 cup milk chocolate chips, 2 Tbsp. Instant coffee granules, 1/2 tsp. baking powder, 1/2 tsp. salt, 1/2 tsp. vanilla extract, 1/2 Tbsp. espresso powder (optional)
Press into a 9x13 inch oven safe baking dish (you can line with parchment paper to make it easier to remove bars from the pan). Use clean hands to press mixture down. Or 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, ~5 minutes. (Keep on low so it doesn't burn the bottom). Remove from heat and stir in the vanilla extract.
1, (14 oz.) can condensed milk (sweetened), 2 tsp. vanilla extract, 2 Tbsp. butter, unsalted
Once the cookie layer is done, pour the condensed milk on top in an even layer. Place back in oven and bake again for 10-15 minutes.
Remove from the oven, it will be bubbling, and sprinkle with sea salt flakes. Let cool for at least 30 minutes - 1 hour. The longer the better so the topping has time to set and not be goopy. You can place in the fridge or freezer to speed this process up. Once the topping has cooled, 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.
2 tsp. flaky sea salt