Don't be afraid of a big wedge of this cake.
Bring honey to a boil in a medium saucepan over medium heat and cook until golden brown and toasty smelling, about 2 minutes. Remove from heat and stir in salt. Carefully pour in cream . The honey will bubble and sputter, so be careful. Stir with a wooden spoon or rubber spatula until homogenous. Let burnt honey mixture cool, then transfer to an airtight container. Cover and chill until cold, at least 3 hours.
Add rhubarb and cook until mixture just starts to bubble again; remove from heat. Cover and let sit until rhubarb pieces are softened but still hold their shape, 70–80 minutes.Cake and assembly Whisk egg yolks, tahini, 6 Tbsp. sugar, and 3 Tbsp. room-temperature water in a small bowl to combine. Add dry ingredients and whisk well; set batter aside.
Using a rubber spatula, add one third of meringue to reserved batter and fold until just streaky, taking care not to deflate meringue. Repeat two more times, dividing remaining meringue in half and mixing the final addition until no streaks remain. Immediately scrape batter into prepared pan and lightly tap pan on counter to evenly distribute and even out size of bubbles.