First make the crust. In a large bowl, sift the flours with the baking soda and salt (if using). Stir in the sugar.
Add the butter and rub it into the flour mixture until it resembles coarse breadcrumbs and there is no dry flour left. This could take 3 to 4 minutes.
Add the lemon juice and stir the mixture with a spatula. Then, a tablespoon at a time, add the ice water and bring it all together into a soft dough. You may not need all of the water, so add it slowly.
Place the dough on a large piece of clingfilm, pat it into a disc, cover and chill for 30 minutes.
Now make the filling. Combine the dates, water and honey in a saucepan. Cover and cook on low heat for 10 minutes until the dates have softened and the mixture is bubbling.
Stir in the walnuts and vanilla and set the mixture aside to cool.
Preheat the oven to 175 C and lightly grease an 8" square baking pan.
Unwrap the cold dough and cut off a third of it. Place the smaller part back in the fridge to use for the criss-cross pattern on top.
Work the larger portion of the dough with your fingers to soften it just a little, then place it in the bottom of the pan. Spread it out evenly, pressing down as you go, making sure it's right up to the corners. The dough is not sticky and will yield easily.
Spread the cooled date mixture on top of the dough, using a spatula to help make an even layer. Place the pan in the fridge so that the crust remains cold and bakes up nice and flaky!
Now get out the smaller portion of the dough and place it on a silicone mat or a floured surface. I like the mat because it prevents sticking and makes clean up easier.
Roll the dough out into a roughly 8 to 9 inch circle. You don't need to be precise, just make sure the circle is wide enough that you can cut strips to fit your baking pan. If you prefer to roll it out into a square or rectangle, that's fine too!
Slice the rolled out dough into even strips and lifting them gently one at a time, place them in a criss-cross pattern on top of the date filling.
Use any remaining dough scraps to cut out cute shapes and patch up any torn bits of the criss-cross pattern.
Bake for 35 to 40 minutes until the crust is browned on top and has puffed up. Let the pan sit at room temperature for at least 30 minutes before cutting into squares and serving with vanilla ice cream! Best stored in the fridge after day one so that the crust doesn't get soft. Happy eating!