Preheat oven to 160 degrees fan forced. Grease and line a 17cm x 28cm slice tray with baking paper, allowing the edges to overhang.
Melt the butter and vanilla in the Thermomix bowl for 3 minutes, Speed 2, 50 degrees.
Add the plain flour, rolled oats, salt, bi-carb soda, brown sugar and raw sugar. Mix for 20 seconds on Reverse, Speed 2. Scrape down the sides. Mix for a further 20 seconds on Reverse, Speed 2.
Spread half of the crumb mixture into the bottom of the prepared tray and press firmly into an even layer. Bake in preheated oven for 15 minutes or until lightly golden. Remove from oven and put aside (leave the oven turned on).
Place the dates into a clean Thermomix bowl. Chop for 10 seconds, Speed 9. Scrape down the sides of the bowl. Add the water, vanilla and butter and mix for 6 minutes, Reverse, Speed 3, 90 degrees. Pour into a bowl and allow to cool slightly.
Pour the date mixture over the cooked oat base and spread out evenly.
Sprinkle the remaining crumble mixture over the top of the date layer. Bake in oven for 23 – 26 minutes or until lightly golden. Remove from oven and allow to cool.
Cover and refrigerate for at least 2 hours (preferably overnight) then take it out and cut into squares.
Store in airtight container in refrigerator or at room temperature for up to 1 week.