Spoon the frozen vanilla frozen custard into medium bowl. Add the salted caramel sauce (recipe below), kouign amann and cocoa nibs. Cover with wrap and transfer the bowl to the freeze for at least 15 minutes and as long as 2 hours.
When ready to serve, gently mash ingredients together with a wooden spoon until just combined. Spoon the Concretes into 2 dessert dishes and serve.
FOR THE SALTED CARAMEL SAUCE: Put sugar and 1/3 cup water into a deep medium pot. Swirl the pot to moisten the sugar. Bring to a boil over medium-high heat, gently swirling the pot often to help dissolve the sugar into a clear syrup.
Boil the syrup until it smokes and just begins to turn a deed caramel brown, 5 to 8 minutes. The syrup will continue to brown very quickly. Be careful it doesn’t bun. When the syrup is uniformly brown, quickly and carefully add the cream, stirring until the sauce is smooth and returns to a boil, about 1 minute. Remove the pot from the heat. Stir in the salt. Caramel sauce will keep, covered and refrigerated, for up to 1 week.