Diffractive optics for nanoscale X-ray imaging, particularly for high energy X-rays, require nanoscale width features with high-aspect ratio thick metal rings (zones) for efficient focusing of X-rays. Electron beam lithography (EBL) has many benefits for producing such structures, allowing patterning of high-resolution and accurately placed structures with placement precisions within a few nanometers over several hundred micrometers. Despite the benefits of EBL, efforts to achieving very high (> 20) aspect ratio structures requires non-standard techniques to overcome issues such as collapse or distortion of the zones and maintaining vertical sidewalls. Methods to increase the effective height of the zones, such as multi-layered lithography and stacking of zone plates present several challenges, such as cost, low yield, and difficult alignment. In this work, we present a new fabrication method, using a single-step-exposure, to pattern both sides of a thin 100 nm membrane to increase the overall effective thickness of a zone plate. By overcoming some of the effects of beam broadening during the electron beam exposure, this process is able maintain provide high-resolution lithography, despite the interfacial membrane layer separating the two resist films. This technique has several advantages, including perfect alignment of the two layers, reduced lithography and fabrication steps, increased mechanical strength and lifetime, producing high-efficiency and resolution zone plates. In this work, double-layer zone plates have been fabricated with outer zone widths down to 25 nm. Results will be presented comparing double-layered zone plates with single-layer zone plates for efficiency and resolution.