  We perform switching current measurements of planar Josephson junctions (JJs)
coupled by a common superconducting electrode, with independent control over
the two superconducting phase differences. We observe an anomalous phase shift
in the current--phase relation of a JJ as a function of gate voltage or phase
difference in the second JJ. This demonstrates a nonlocal Josephson effect, and
the implementation of a $\varphi_0$-junction which is tunable both
electrostatically and magnetically. The anomalous phase shift was larger for
shorter distances between the JJs and vanished for distances much longer than
the superconducting coherence length. Results are consistent with the
hybridization of ABSs, leading to the formation of an Andreev molecule. Our
devices constitute a realization of a tunable superconducting phase source, and
could enable new coupling schemes for hybrid quantum devices.
