For the cookies:

1. Pre-heat the oven to 170 C (350 F). Line three baking trays with parchment paper.
2. Place the sesame seeds on one of the baking trays. Toast in the oven until golden brown and fragrant. Remove from the oven and let cool.
3. In a medium sized bowl, whisk together the flour, baking soda and salt.
4. In the bowl of a stand mixer fitted with the beater attachment, beat the butter and sugars on medium speed until light and fluffy, 3 minutes. Add in the egg, vanilla and sesame oil and beat until combined. Pause mixing to scrape down the bottom and sides of the bowl.
5. Set the mixer speed to low then add in the flour mixture. Beat until just combined.
6. Add in the chocolate and sesame seeds and mix until evenly distributed.
7. Cover the bowl with plastic wrap and chill until firm, 30 minutes to an hour.
8. Once chilled, use an ice-cream scoop to scoop the cookie dough into balls and onto the prepared baking trays, about 70 grams (2.5 ounces) per cookie dough ball and 4 cookies per sheet. Sprinkle the tops with the flaked salt then place the trays in the fridge, or freezer until the dough is firm.
9. Bake for 10 to 13 minutes, or until golden brown and the edges are crisp but the middles are still slightly soft.
10. Let cool on the baking trays for 10 minutes before moving out onto a wire rack to cool completely before filling with the buttercream and stacking.

For the buttercream:

1. Place the butter and tahini in the bowl of a stand mixer fitted with the beater attachment. Beat on medium speed until light and fluffy.
2. Add in the cream, vanilla and salt then beat until smooth.
3. Lower the mixer speed and beat in the confectioners’ sugar until just combined.
4. Pause mixing to scrape down the bottom and sides of the bowl then increase the speed back to medium and beat until light and fluffy, 4 minutes.
5. Beat in the halva chunks until evenly distributed.

For assembly:

1. When you are ready to assemble the cake, set aside 10 of the best looking, and evenly shaped cookies. Place the first cookie on a cake stand or serving plate.
2. Spread a generous tablespoon of the buttercream over the face then top with another cookie, pressingly gently down to sandwich. Repeat this filling, stacking and pressing process until all of the cookies and buttercream have been used up.
3. Move the cookie cake to the refrigerator to chill for 30 minutes or until the buttercream has firmly set.
4. Use a warm knife to slice and serve.