Instructions

for the panna cotta

Line fine-mesh strainer with 3 layers of cheesecloth, leaving 6 inches overhang on all sides, and set over medium bowl. Process beets in food processor for 30 seconds. Stop processor, scrape down sides of bowl, then continue processing until beets form pulpy paste, 30 to 60 seconds longer. Transfer beet paste to prepared strainer and allow beet juice to drain into bowl. Gather overhanging cheesecloth and squeeze beets to release as much juice as possible (you should have about 1 cup juice).Optional but highly recommended: Adjust oven rack to middle position and heat oven to 200 degrees F/93 degrees C. Line rimmed baking sheet with parchment paper. Spread beet pulp in even layer on prepared sheet and transfer to oven. Bake until dry and crunchy, 1 to 1½ hours. Transfer ¼ cup beet crumbs to small bowl; set aside. Remaining beet crumbs can be transferred to airtight container and stored at room temperature for up to 1 week. (Try the extra beet crumbs sprinkled on salads or hummus.)
Transfer ¾ cup beet juice to medium saucepan. Transfer remaining ¼ cup beet juice to small bowl. Sprinkle gelatin evenly over surface of beet juice in bowl; let stand for 10 minutes to hydrate gelatin.
Add cream, sugar, and salt to beet juice in saucepan and whisk to combine. Cook over medium-low heat, whisking frequently to dissolve sugar, until mixture registers 140 degrees F/60 degrees C, about 5 minutes. Add beet juice–gelatin mixture to saucepan, whisking to dissolve gelatin and break up any clumps, and continue cooking until mixture registers 150 degrees F/66 degrees C, 1 to 2 minutes longer. Remove saucepan from heat and strain mixture through fine-mesh strainer into large measuring cup or pitcher.
Let panna cotta base cool to 105 degrees F/41 degrees C. Add buttermilk and whisk to combine. Set 4, 5, or 6 small bowls on baking sheet. Divide base evenly among bowls. Cover sheet in plastic wrap, making sure that plastic does not touch surface of panna cottas; refrigerate until just set (mixture should wobble when shaken gently), about 4 hours. Panna cottas can be refrigerated for up to 24 hours.

for the black sesame brittle

Line rimmed baking sheet with reusable silicone pan liner. Combine sesame seeds, sugar, and honey in small skillet. Cook over medium heat, stirring constantly with rubber spatula, until mixture has sandy texture, 1 to 2 minutes. Continue to cook, stirring frequently, until sugar melts and caramelizes, 1 to 2 minutes longer. Off heat, stir mixture until seeds are evenly coated and then quickly transfer to prepared sheet. Spread into thin, even layer and let cool at room temperature until sugar hardens, 5 to 10 minutes.
Using your hands, break sesame brittle into ¼-inch pieces. Combine brittle and ¾ teaspoon flake sea salt. (If you made the optional beet crumbs: Combine brittle, beet crumbs, and 1 teaspoon flake sea salt.) Sesame brittle can be stored in airtight container for up to 1 week. Sprinkle top of each panna cotta evenly with sesame brittle and serve.