Preheat an oven 170°c/150°c fan (338°f/302°f).
Line a 2lb loaf tin with baking parchment (or use a loaf tin liner) then set aside.
Roughly chop up the dates & ginger (if using) then place into a bowl. Add in the bicarbonate of soda & boiling water then leave to soak for 10-15 minutes, to soften.
Next, sift the flour, baking powder, ginger, cinnamon & salt into a bowl then set aside.
Place the softened butter & sugar into the bowl of a stand mixer then use the paddle attachment to beat until light & fluffy. This will take around 5 minutes on a medium speed.
With the mixer still running on a medium speed, beat in the eggs one at a time then mix in the treacle.
Next, blitz the soaked dates up with a stick blender, to make a puree.
Add in half of the flour & half of the date puree into the batter & mix until just combined.
Scrape down the sides of the bowl with a spatula then add in the remaining flour, dates & the buttermilk. Mix until just combined.
Transfer the cake batter to the lined loaf tin then pipe a thin line of softened butter down the middle.
Bake in the preheated oven for 45-50 minutes. Once cooked, a skewer inserted into the middle will come out clean.
Let the cake cool in the tin for 5 minutes then carefully transfer to a cooling rack & leave to cool completely. Once cool, place the cake into an airtight container (or wrap in clingfilm), leave to mature overnight then cut into thick slices.