Pre heat oven to 160c and prepare your pans by lining the bottom with baking paper and spraying with cooking oil. I used 2 x 6 inch pans with 3 cups of batter in each (alternatively you could use 2 x 8 inch pans with 3 cups of batter in each or 3 x 8 inch pans with 2 cups of batter in each).
Pit your dates and roughly chop them, measure out 3 cups after chopping.
Place you dates, water and bicarb soda in a food processor. Make sure all the dates are covered. Leave dates to steep for 10 minutes.
While waiting for the dates, beat sugar and butter in a mixer on a medium speed until thick and creamy.
Process date mixture and add to the butter and sugar.
Beat till the dates are mixed through.
Add in eggs and vanilla and mix till incorporated.
Add in flour and beat until just combined.
Pour your batter into your prepared pans. Place in the oven and bake for 40 minutes. If you're using 8 inch pans, then check your cakes at the 30 minute mark. Put a skewer or thin knife into the cake and make sure there is no wet batter that sticks to it (you may get cooked crumbs, which is fine).
Leave your cakes to cool.