Preheat Oven: Preheat your oven to 350°F (175°C).
Prepare Date Mixture: In a large bowl, combine the chopped dates, hot coffee or espresso, and baking soda. Set aside to soak.
Mix Dry Ingredients: In a small bowl, whisk together the flour, cinnamon, nutmeg, and salt.
Cream Butter and Sugars: Using a mixer, cream the softened butter with the brown sugar and granulated sugar until light and fluffy.
Add Egg and Vanilla: Beat in the egg and vanilla extract until combined.
Combine Wet and Dry Ingredients: Strain the date mixture, setting the dates aside. Alternately add the reserved liquid from the date mixture and the flour mixture to the butter mixture in three parts, beginning and ending with the liquid. Mix until smooth.
Fold in Dates and Walnuts: Gently fold in the soaked dates and toasted walnuts.
Prepare the Pan: Grease a 9×5-inch loaf pan with butter or baking spray. Line with parchment paper, ensuring the paper covers the bottom and sides, and spray the parchment.
Bake: Pour the batter into the prepared loaf pan and bake for 55-65 minutes, or until a toothpick inserted into the center comes out clean.
Cool: Allow the cake to cool for 20 minutes before removing it from the pan. Carefully peel off the parchment paper and transfer the cake to a wire rack to cool completely.
To Make the Coffee Glaze:
Dissolve Espresso: Combine hot water with the instant espresso and stir until fully dissolved.
Mix Glaze: In a small bowl, whisk together the powdered sugar, melted butter, vanilla extract, and the prepared espresso. Adjust the consistency by adding ½ teaspoon of hot water at a time, if needed.
Drizzle and Garnish: Drizzle the espresso glaze over the cooled coffee cake. Scatter additional toasted walnuts on top, if desired. Let the glaze set before slicing.