One-exposure HDR

I took this picture of an old barn yesterday but my second exposure for the HDR was way off so I made an HDR image with only one, underexposed photo. How did I do it? Since I was shooting in RAW mode, I made two copies of the photo when I processed it: one with a very high positive exposure adjustment. Then I merged them back into one photo in Photoshop. Kind of feels like cheating doesn't it?

After (above), Before (below)