Preheat the oven to 320°F (160°C, convection). Butter and line a 9-inch loaf pan (about 22 cm).
Warm the honey, brown sugar, and milk together in a small saucepan over low heat, stirring until smooth. Do not boil. Remove from heat and let cool slightly.
In a large bowl, whisk together the flours, baking powder, baking soda, salt, spices, and orange zest.
Gradually pour the warm honey mixture into the dry ingredients, whisking gently until you obtain a smooth, glossy batter.
Add the egg, melted butter, and walnut liqueur (or your chosen substitute). The batter should have the texture of thick cream.
Pour into the prepared pan and smooth the surface. Bake for 55 to 60 minutes, until golden brown and a knife inserted in the center comes out clean.
Let cool for 10 minutes, then remove from the pan and transfer to a wire rack. Once completely cool, wrap the loaf in parchment paper or a clean linen cloth and let it rest for at least 24 hours before slicing. This resting time allows the flavors to deepen and the crumb to become soft, moist, and beautifully aromatic.