Preheat the oven to 180°C / 350°F / Gas Mark 4, no fan (if you have convection oven reduce the temperature by 20° or follow the manufacturer's instructions).
Prepare a rectangular 21x21 cm / 8x8 inch pan (measured at the bottom, I used a brownie pan), grease it lightly with butter and line it with baking paper.
POT: In a medium pot melt the butter, take the pot off the heat, add honey, orange zest, and finely chopped chocolate, stir until melted. Add the eggs and whisk until combined.
BOWL: In a large bowl, mix all the dry ingredients - sifted wheat and rye flour, sugar, ground nuts, cocoa, gingerbread spice, baking soda, salt.
Add the content of the pot to the mixed dry ingredients in the bowl, gently mix with the spatula, but not for too long, only until just combined.
BAKE: Pour the batter into the prepared baking pan, smooth out the top, tap the pan slightly (to remove any air bubbles).
Bake for 20-25 minutes. The cake is ready when a cake tester/bamboo skewer inserted into the middle of the cake comes out clean.
Take the cake out of the pan a leave to cool (it doesn't have to be completely cooled). In the meantime, prepare the chocolate glaze.