Preheat the oven to 350°F. Lightly grease an 8 1/2" x 4 1/2" loaf pan., Place the dates, butter, baking soda, salt, and brown sugar in a mixing bowl. Pour the hot coffee into the bowl, stirring to combine. Allow the mixture to cool for 15 minutes., Add the egg, vanilla, liquor, baking powder, and flour, beating gently until smooth. Stir in the walnuts., Pour the batter into the pan, gently tapping the pan on the counter to settle the batter., Bake the bread for 45 to 55 minutes, tenting the loaf gently with foil after 30 minutes, to prevent over-browning. Remove the bread from the oven; a cake tester or toothpick inserted into the center should come out clean, and an instant-read thermometer should read about 200°F., After 10 minutes, gently turn the bread out of the pan onto a rack to cool. Cool completely before slicing. Wrap airtight, and store at room temperature for several days; freeze for longer storage.