1. Preheat the oven to 180C fan and grease a square tin (20x20cm) well with butter. You can line the tin with baking paper if you'd rather, it can be a bit tricky to spread the oat mixture on top.
2. Place the dates in a saucepan with the 150ml of water and place over a medium heat, cooking gently for 5-10 minutes. You want the dates to be nice and squishy to make a spreadable paste. Even if you have chosen stoned dates, there can be a few stones that remain, look out for any and remove where needed. Leave this date puree to cool.
3. In a large mixing bowl, add the dry ingredients and mix. Next, add the cold water to the bowl and use your hands to bring together to form a dough. If the dough seems too dry you might need to add a little more water, but add slowly as you don't want it to be too sticky either.
4. Press half of this dough mixture in the bottom the prepared tin, then top with the date puree, followed by the remaining oat dough mixture. Press down firmly.
5. Bake for 30 minutes, the top will be a very slight pale golden colour and you'll have a wonderful biscuit smell coming from the oven!
6. Cool in the tin, then using a sharp knife, cut into slices and remove with a spatula.
Delicious warm with a cup of tea or even as a pudding with cream on top. equally good cold!
These slices freeze well, it's worthwhile doubling the recipe so you have some in the freezer.