The steepness of an openpit mine's slopes has a substantial influence on the mine's financial return. This paper proposes a novel design methodology where overall steeper pitwalls are employed without compromising the safety of the mine. In current design practice, pitwall profiles are often planar in cross section within each rock layer: that is, the profile inclination across each layer tends to be constant. Here, instead, a new geotechnical software, OptimalSlope, is used to determine optimal pitwall profiles of depth-varying inclination. OptimalSlope seeks the solution of a mathematical optimization problem where the overall steepness of the pitwall, from crest to toe, is maximized for an assigned lithology, geotechnical properties and factor of safety (FoS). Bench geometries - bench height, face inclination, minimum berm width - are imposed in the optimization as constraints that bind the maximum local inclination of the sought optimal profile together with any other constraints, such as geological discontinuities, that may influence slope failure. The obtained optimal profiles are always steeper than their planar counterparts - that is, the planar profiles exhibiting the same FoS - up to 8 degrees, depending on rock type and severity of constraints on local inclinations. The design of a copper mine is first carried out with planar pitwalls, and then adopting the optimal pitwall profiles determined by OptimalSlope. The adoption of optimal slope profiles leads to a 34 percent higher net present value (NPV), and reductions of carbon footprint and energy consumption of 0.17 Mt of carbon dioxide equivalent (CO2eq) and 82.5 million MJ, respectively, due to a 15 percent reduction of rockwaste volume.