  We consider the Monge-Kantorovich problem between two random measuress. More
precisely, given probability measures
$\mathbb{P}_1,\mathbb{P}_2\in\mathcal{P}(\mathcal{P}(M))$ on the space
$\mathcal{P}(M)$ of probability measures on a smooth compact manifold, we study
the optimal transport problem between $\mathbb{P}_1$ and $\mathbb{P}_2 $ where
the cost function is given by the squared Wasserstein distance $W_2^2(\mu,\nu)$
between $\mu,\nu \in \mathcal{P}(M)$. Under appropriate assumptions on
$\mathbb{P}_1$, we prove that there exists a unique optimal plan and that it
takes the form of an optimal map. An extension of this result to cost functions
of the form $h(W_2(\mu,\nu))$, for strictly convex and strictly increasing
functions $h$, is also established. The proofs rely heavily on a recent result
of Schiavo \cite{schiavo2020rademacher}, which establishes a version of
Rademacher's theorem on Wasserstein space.
