How to Make It
Preheat oven to 350°F with oven rack in middle of oven. Stir together graham cracker crumbs, sesame seeds, sugar, and salt in a large bowl. Add melted butter; stir to moisten. Press mixture firmly and evenly into bottom and up sides of a 9 1/2-inch tart pan. Place on a rimmed baking sheet, and bake in preheated oven on middle rack until crust is firm and appears dry, 12 to 15 minutes. Set aside to let cool completely, about 10 minutes.
Meanwhile, place chopped chocolate in a medium heatproof bowl. Place miso in a small fine wire-mesh strainer, and set both near the stove. Bring cream to a simmer in a small saucepan over medium-high. Remove pan from heat, and immediately submerge strainer of miso in the hot cream. Quickly stir and mash miso against the strainer to dissolve, discarding any remaining solids in strainer. Pour hot miso cream over chopped chocolate. Let stand about 1 minute. Stir with a spatula just until melted and smooth.
Pour chocolate mixture into cooled crust. Gently shake or tap the tart pan to spread the chocolate mixture into an even layer. Sprinkle black sesame seeds around the edge of the tart. Refrigerate, uncovered, until set, 3 to 4 hours.
Remove tart from tart pan. Let tart come to room temperature before serving, at least 45 minutes. Use a hot knife to cut tart into 12 slices. Serve with whipped cream, if desired.