Preheat oven to 175°C. Line 20cm round or square pan.
Mix flour, baking powder, baking soda, and salt.
Blend applesauce, date paste, coffee, vanilla, and apple cider vinegar until smooth.
Fold wet into dry until just combined. Fold in walnuts.
Pour batter into prepared pan and bake until a skewer comes out clean.
Cool completely.
For frosting: blend all ingredients (last five) until smooth, heat until thickened, cool completely before spreading.