Make the pots de crème: Position a rack in the middle of the oven and preheat the oven to 300oF (150 ̊C). Put six (6-ounce/180-ml) ramekins into a baking pan.
Bring the cream and milk to a boil over medium heat in a small saucepan and then remove from heat. Add the vanilla bean seeds and pod, cover, and infuse while you prepare the custard.
In a medium saucepan, melt the butter over medium heat. Whisk in the brown sugar. Cook, without stirring, for about 5 minutes or until the mixture is amber hued, the consistency of sand, and smells mildly nutty. Discard the vanilla pod and slowly whisk in the cream and milk over low heat until the sugar has dissolved. Remove from the heat and stir in the salt.
Bring a kettle of water to a boil and then set it aside. In a large bowl, whisk the egg yolks until they are pale and thickened, about 3 minutes. Add the cream mixture in a slow, steady stream, stirring constantly, until it’s fully combined with the yolks. Strain the custard through a fine-mesh sieve into a bowl, then divide it evenly among the ramekins; each one should be about three- quarters full. Skim away any foam from the surface. Fill the baking pan with the hot water until it comes halfway up the sides of the ramekins. Cover the pan with foil and prick the foil with a fork. Bake for 45 minutes to 1 hour, or until the custards are set on the sides but still jiggle in the center. Transfer the ramekins to a wire rack and cool to room temperature. Cover each ramekin with plastic wrap and refrigerate at least 4 hours or up to overnight.
Make the caramel sauce: In a medium saucepan, heat the sugar and 2 tablespoons water over medium heat. Cook, swirling occasionally, until the sugar has dissolved. Increase the heat to medium-high and bring the liquid to a boil, gently swirling but never stirring it. If the sugar starts to crystallize, use a pastry brush dipped in water to wipe down the sides of the pan. After about five minutes, when the sugar is deep amber, remove it from the heat and whisk in the cream, butter, salt, tahini, and lemon juice. Set aside and let it cool to room temperature.
Before serving, bring the custards to room temperature. Sprinkle with flaky sea salt and serve topped with a dollop of whipped cream, a drizzle of caramel sauce, a sprinkle of toasted kasha, and sesame seeds.
