For the crust: Preheat oven to 350 F. Line an 8-by-8-inch square pan with enough parchment paper to have 1-inch wings on 2 sides.
In a stand mixer fitted with a paddle, combine the butter, sugar, vanilla and salt and beat on medium until pale and fluffy. Reduce to low, add both flours and mix to combine. Press evenly into the pan and bake for 10 minutes. Let cool slightly, about 10 minutes, while you make the filling.
For the filling: In a large bowl, toss the apples with the lemon juice. Sprinkle in the flour, sugar, cinnamon, cardamom, nutmeg and salt and toss to combine. Arrange evenly on top of the crust.
For the crumble: In a medium bowl, combine the flour, sugar, cinnamon and salt. Add the butter and mix with your hands until crumbly. Sprinkle all over the apples. Sprinkle on the halva or marzipan and sprinkles, if using. Bake until the crumbles begin to brown, 35 to 40 minutes. Let cool in the pan completely, about 1 hour and then slice into bars. Enjoy!