The paper presents a novel optomechanical system that addresses the challenges of integrating sensitive micromechanical elements into high-finesse cavities. The system features a 50 nm thick dielectric membrane placed between two macroscopic, rigid, high-finesse mirrors, allowing for direct measurement of the square of the membrane's displacement, which can be used to read out the membrane's energy eigenstate. This approach avoids the technical challenges of integrating high-quality mirrors into micromachined devices, such as mechanical loss and size constraints. The authors demonstrate laser cooling of the membrane's Brownian motion and estimate the feasibility of observing quantum jumps of the mechanical system. They show that the system can achieve a signal-to-noise ratio sufficient for observing quantum jumps, making it a promising platform for studying quantum effects in optomechanical systems.The paper presents a novel optomechanical system that addresses the challenges of integrating sensitive micromechanical elements into high-finesse cavities. The system features a 50 nm thick dielectric membrane placed between two macroscopic, rigid, high-finesse mirrors, allowing for direct measurement of the square of the membrane's displacement, which can be used to read out the membrane's energy eigenstate. This approach avoids the technical challenges of integrating high-quality mirrors into micromachined devices, such as mechanical loss and size constraints. The authors demonstrate laser cooling of the membrane's Brownian motion and estimate the feasibility of observing quantum jumps of the mechanical system. They show that the system can achieve a signal-to-noise ratio sufficient for observing quantum jumps, making it a promising platform for studying quantum effects in optomechanical systems.