NOVELTY - The method involves transferring heat through a header plate (17) between one of fluids traveling along a pass of a flow path and other fluid traveling along another pass of another flow path. The heat is transferred through the plate between the former fluid traveling along the latter pass of the former flow path and the latter fluid traveling along the former pass of the latter flow path. The heat is transferred through the plate between the former fluid traveling along the former pass of the former path and the latter fluid traveling along the former pass of the latter path.    USE - Method for operating a heat exchanger i.e. recuperative heat exchanger (claimed) to optimize an overall system efficiency of a high temperature application such as gas turbine and high temperature fuel cell system.    ADVANTAGE - The method allows the heat exchanger with high heat exchanger effectiveness while the exchanger provides reduced cost and complexity over previous designs. The method enables usage of multiple passes within the heat exchanger to enable a long counter-flow heat exchange length without requiring a long and narrow package, thus allowing the heat exchanger to be packaged into a smaller space in a system requiring such a recuperator. The method allows reducing complexity by using few tubes and achieving multiple flow passes within each tube, thus minimizing a number of fluid sealing joints. The method allows manufacturing a heat exchange core by using a furnace brazing operation, thus reducing cost of manufacture. The method enables usage of heat transfer augmentation surfaces such as flow baffling features for the fluid resulting in a parts count reduction with inherent cost benefits. The method allows attaching heat transfer enhancement features via a metallurgical bond to a set of thermally conductive walls in order to improve the rate of heat transfer through the walls. The method allows incorporating an ability to bypass a portion of one of the flows in order to more precisely control the resulting temperature.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for a recuperative heat exchanger comprising a plate partially defining a flow path.    DESCRIPTION OF DRAWING(S) - The drawing shows a perspective view of a heat exchanger core from a heat exchanger.    Flattened tubes (15)    Header plates (16, 17)    Flow baffle (18, 19)    Triangle-shaped inlet manifolds (21, 22)    Heat exchange region (44)