In complex terrains, wind farm optimisation requires a sophisticated approach due to increased flow complexity. This study integrates the precision of high-fidelity Large Eddy Simulations (LES) with the efficiency of Bayesian Optimisation (BO) to systematically evaluate and refine turbine layouts around a 2D hill. The wind farm simulator WInc3D is employed to perform high-order LES of the atmospheric boundary layer together with an immersed boundary method and a wall model to reproduce the terrain features, while actuator discs are used to parameterise the wind turbines. WInc3D, part of the high-order finite-difference framework Xcompact3d, offers a highly efficient parallelisation strategy with "spectral-like" accurate numerical schemes on a Cartesian mesh. This simulation environment has been successfully validated on a steep hill with a constant section, examining the performance of wind turbines around it and comparing it against previously published experimental and numerical data. While LES provides the means to resolve the nonlinear and unsteady flow dynamics of atmosphere-to-wake and wake-to-wake interactions, its high computational demands limit its direct application in optimisation tasks. To overcome this, BO offers a probabilistic model, optimising the evaluation process and thus making comprehensive LES evaluations viable for optimisation endeavours. This study focuses on comparing a conventional two-turbine layout around the hill against two optimised configurations, BO1 and BO2, each resulting from distinct optimisation processes. Both BO1 and BO2 have four design variables each. In BO1, the variables encompass the streamwise locations and hub heights of both turbines. In contrast, BO2 introduces the disc tilt angle of the upstream turbine as a new variable, while fixing the upstream turbine's hub height. The BO1 configuration benefits from an elevated upstream turbine hub, leading to a marked power increase in the downstream turbine. Conversely, BO2 maintains a more modest hub height for the upstream turbine, but the addition of disc tilt contributes to substantial power gains, benefiting from wake steering. Notably, approximately a 9-degree tilt angle results in a roughly 4.5\% boost in total power compared to the same layout without tilt.