I was a little intimidated at first to make halva, given that the process is more like making candy than like making cake, but it was worth it. I definitely recommend a candy thermometer here! I would only make one change, which is to reduce the amount of sesame seeds on top – I was supposed to use 2 tablespoons, but I used 1 1/3 tablespoons and, even then, I felt it was a bit too much. I’d say no more than 1 tablespoon, and even that is optional; I’ve made the change below. That being said, this was absolutely delicious! It was a big hit with our family, and I’ll have to make it again.
1 ½ cups tahini
¼ tsp. kosher salt
3 Tbsp. black and white sesame seeds, divided
1 ½ cups sugar
½ cup water
4 oz. bittersweet chocolate
¼ cup dried edible flowers (such as cornflowers and/or roses; optional, and I did not use them)
flaky sea salt
Lightly coat an 8½x4½" loaf pan with nonstick spray and line with parchment paper, leaving a 2" overhang on both of the long sides.
Mix tahini, kosher salt, and 2 Tbsp. sesame seeds in a medium, heat-resistant bowl to combine; set tahini mixture aside.
Cook sugar and water in a small saucepan over low heat, stirring with a heatproof rubber spatula, until sugar is dissolved, about 4 minutes. Increase heat to medium-high and fit pan with candy thermometer. Cook syrup, brushing down sides of saucepan with a wet pastry brush as needed to dissolve any crystals that form, until thermometer registers 250°, 7–10 minutes. Immediately remove syrup from heat and gradually stream into reserved tahini, mixing constantly with spatula. Continue to mix just until halva comes together in a smooth mass and starts to pull away from the sides of bowl (less than a minute). Be careful not to overmix or halva will be crumbly. (I think I may have overmixed by one or two turns of the spoon, but it did was still great.) Working quickly, scrape into prepared pan and let cool.
Melt chocolate in a heatproof bowl set over a pan of simmering water (do not let bowl touch water), stirring often. Remove from heat. Invert halva onto a wire rack set inside a parchment-lined rimmed baking sheet (honestly, I would just reuse the parchment from the pan here, after inverting the halva out of it); peel away and discard parchment. Pour chocolate over halva and sprinkle top with flowers (if using), sea salt, and remaining sesame seeds. Let sit until chocolate is set before serving, about 30 minutes. (Halva can be stored at room temperature, tightly wrapped, for a few days.)