In a small saucepan over low heat, melt the ghee and coconut butter. Remove from the heat. Add the tahini, cacao powder, maple syrup, and salt. Whisk to combine.
Transfer the mixture to a glass 8-inch (2 L) square baking dish. Cover and place in the freezer for at least 2 hours.
Remove from the freezer and let sit for 10 minutes at room temperature to soften.
Meanwhile, heat a dry, medium skillet over medium heat. Add the sesame seeds in a single layer. Toast, tossing occa- sionally, until the sesame seeds are fragrant and lightly browned, 4 to 5 minutes.
To serve, slice the fudge into 16 squares. Drizzle with tahini. Sprinkle with toasted sesame seeds and flaky sea salt, if using. Enjoy immediately. Store the fudge in an airtight container in the freezer for up to 1 month.