  Detecting entanglement in many-body quantum systems is crucial but
challenging, typically requiring multiple measurements. Here, we establish the
class of states where measuring connected correlations in just $\textit{one}$
basis is sufficient and necessary to detect bipartite separability, provided
the appropriate basis and observables are chosen. This methodology leverages
prior information about the state, which, although insufficient to reveal the
complete state or its entanglement, enables our one basis approach to be
effective. We discuss the possibility of one observable entanglement detection
in a variety of systems, including those without conserved charges, such as the
Transverse Ising model, reaching the appropriate basis via quantum quench. This
provides a much simpler pathway of detection than previous works. It also shows
improved sensitivity from Pearson Correlation detection techniques.
