All-oxide composites are increasingly investigated in the field of microelectronics and telecommunications because of their multifunctionalities. Advanced control of interfaces is required to fully tune the macroscopic properties of the composites. Processing ferroelectric Ba0.65Sr0.35TiO3 (BST65/35)-TiO2 composites by Spark Plasma Sintering (SPS), we show that the SPS electric current promotes an interphase growth whose thickness depends on the BST/TiO2 stacking and on the current direction. In all cases, the interface is composed of Ba-1.14(2) Ti8O16- a highly defective, but stable phase which can be used to tune the overall dielectric properties of the composites.