To make the cake, heat the oven to 350°F with a rack in the middle position. Mist a 9-by-5-inch loaf pan with cooking spray, then line it with an 8-by-14-inch piece of kitchen parchment, allowing the excess to overhang the long sides of the pan. Mist the parchment with cooking spray.

In a medium bowl, whisk together the flour, salt, baking powder and baking soda. In a medium microwave-safe bowl, microwave the chocolate on 50 percent power, stirring every 15 seconds, until melted and smooth. Whisk in the tahini and cocoa powder until smooth; set aside.

In a stand mixer with the paddle attachment, beat the butter and sugar on medium-high until light and fluffy, about 5 minutes. With the mixer running, add the eggs one at a time, scraping the bowl after each addition. Add the vanilla and mix until fully incorporated. With the mixer running on low, add about one-third of the flour mixture followed by about half of the yogurt. Next, add about half of the remaining flour mixture, then the remaining yogurt and finally the remaining flour mixture. Mix on low until just combined, about 1 minute. Fold the batter a few times with the spatula to ensure no pockets of flour remain.

Transfer half of the batter (about 2 cups) to the bowl with the chocolate-tahini mixture. Using a silicone spatula, gently fold until homogeneous. Pour about half of the chocolate batter into the center of the prepared pan; do not spread it. Working quickly, pour in about half of the plain batter followed by the remaining chocolate batter and, finally, the remaining plain batter. Insert a butter knife vertically at one end of the pan until the tip touches the bottom, then swirl the batters by dragging the knife in a swishy zigzag motion to the other end of the pan. Smooth the top with a spatula and rap the pan against the counter to remove any air bubbles.

Bake until the top is deeply browned and a toothpick inserted at the center of the cake comes out with a few small crumbs attached, 50 to 60 minutes. Cool the cake in the pan on a wire rack for 15 minutes. Lift the loaf out of the pan using the parchment and set it directly on the rack. Cool for at least 1 hour.

To make the glaze, in a 2-cup liquid measuring cup, combine the chocolate, tahini, butter and salt. Microwave on 50 percent power, stirring every 15 seconds, until the butter is melted and the chocolate is soft and beginning to melt, about 1 minute. Whisk until smooth and emulsified; the glaze should have the consistency of pourable yogurt. If it is too thick, whisk in water 1 teaspoon at a time.

Drizzle the warm glaze onto the cake, allowing it to run down the sides. (If the glaze cools before pouring, warm it in the microwave on 50 percent power just until pourable, about 10 seconds.) Sprinkle the top of the cake with the sesame seeds. Let the glaze set for about 1 hour before slicing and serving.