We have demonstrated a low-cost monolithic approach to fabricating micro-mirror platforms with tunable flatness for applications including Optical Coherence Tomography (OCT). This method enables flat, light-weight micro-mirrors with high resonance frequency to be made out of a single silicon-on-insulator (SOI) wafer, enabling a 10X improvement in mirror flatness over prior monolithic constructions. Using a single backside mask and etch, we take advantage of the aspect-ratio-dependent etch rate (ARDE) of deep reactive ion etching (DRIE) to simultaneously form both a support frame and a two-axis scanning micro-mirror. The mirror has a diameter of 1mm, while the thicknesses of the frame and the mirror (which has a conical backside profile) are 500μm and ~100μm, respectively.