Preheat oven to 350F. Line 2 jelly roll pans (12" x 17") with parchment paper and set aside.
With the paddle attachment of a stand mixer beat together the eggs, oil, sugar and vanilla extract until fully combined.
In a separate bowl sift together the all purpose flour, whole wheat flour, baking soda, baking powder, salt, cinnamon and cardamom.
Fold in the carrots, raisins and walnuts**. Let the cake rest for 10 minutes to allow the moisture of the batter to soften the whole wheat flour.
Divide the batter evenly between the two jelly roll pans in a thin layer. Bake for 15-17 minutes or until fully baked through - good clue: you should be able to smell the deliciousness of the cake when it's just about done.
Remove cakes from the oven and allow to cool completely.
*Optional but totally worth it: In a medium skillet over medium heat toast the flours for 6-7 minutes - should smell lightly nutty and almost like popcorn. Adds a toasty, nutty depth of flavor to an already warm and comforting cake.
**Also optional, but you might be sad if you don't: Toast the walnuts in an oven at 350F for 10 minutes before chopping.
Tahini Buttercream (adapted from Molly Yeh)
While the cakes are cooking start making your buttercream. With a hand mixer or a stand mixer with the whisk attachment beat the butter and tahini together until smooth. While mixing add in the powdered sugar, cardamom, and salt. Continue to beat until completely smooth and slightly lightened in color, about 1-2 minutes on medium speed.
Using a ring mold cut out as many circles as you can. With either a piping bag or a small offset spatula frost each circle with the icing. Stack cakes 2 high and top off with the sesame seeds and za'atar.