Preheat oven to 350 F. Grease a 13-in by 9-in baking pan, set aside.
For the Crust: In a large bowl, combine the flour, crushed walnuts, oats, brown sugar, cinnamon, baking soda, and salt. Cut in the cold butter until crumbly. (You have to work fast so the butter does not warm too quickly.)
For the Filling: In a medium size bowl, whisk together the eggs and brown sugar until well blended, and close to ribbon stage. Add vanilla, stirring to combine. Fold in the chopped dates. (can be finely chopped by hand or pulsed in food processor).
Press 3/4 of the crust mixture into the prepared pan. Pour the filling over the first crust layer, making sure to spread evenly over all surface. Add the 1/2 cup of chopped walnuts to remaining crust mixture. Evenly distribute the last of the crust mixture over the filling.
Bake for 25 – 30 minutes, until lightly browned. Cool completely on a wire rack before cutting into squares.
Store in an airtight container for up to one week. For longer shelf-life, store in the refrigerator.
Crust can be made in a food processor, but be careful not to over-mix.