Heat oven to 350 degrees Fahrenheit and position middle rack in the center of the oven.
Create either an aluminum foil or parchment paper sling by folding sheets of aluminum foil/parchment paper into strips that are 8 inches wide to cover the bottom of the baking dish. Position them perpendicular to one another with the ends hanging over the pan. Make sure to push foil/parchment paper flush to the pan. Grease the pan and foil/parchment paper with butter and flour, then set aside.
In the food processor, pulse the flour, baking powder, salt, brown sugar, and pecans until mixture resembles course cornmeal (about 5-8 pulses). Add the butter and pulse until the mixture looks like sand (about 8-9 pulses). Add the water and espresso powder, pulse again (about 3-4 pulses) to even mix.
Press mixture into the 8x8 inch baking pan using the back of a measuring cup.
Bake for about 25 minutes. Crust should be light brown on the top and spring back when touched.
Remove from oven and let cool.
Filling:
As the crust is baking, whisk together the melted butter, corn syrup, brown sugar, vanilla, dark rum, and salt.
Once combined, add the egg and whisk until incorporated.
Bar Assembly:
Pour filling over the cooled crust, sprinkle chocolate chips and then pecans evenly over the top. Gently press pecans into the filling mixture.
Bake for about 22-25 minutes, the top should be brown across the surface.
Cool for minimum 1 hour on a wire rack.
To remove from pan, loosen edges with a knife, then gently lift using the ends of the aluminum foil/parchment paper sling.
Cut into 2x2 inch bars.
Cover with plastic wrap or plastic bag and store in the refrigerator for 3-4 days.
Notes
*CONSUMING RAW OR UNDERCOOKED MEATS, POULTRY, SEAFOOD, SHELLFISH, OR EGGS MAY INCREASE YOUR RISK OF FOODBORNE ILLNESS, ESPECIALLY IF YOU HAVE CERTAIN MEDICAL CONDITIONS.