Air carrier Captain reported encountering severe turbulence climbing out of DEN that resulted in short periods of aircraft control difficulties.

Narrative

On climb out of Denver we were deviating around convective weather. ATC had us level at 12;000 feet. We were in clear air between cells and the ride was variable between constant light turbulence and moderate chop. The ride instantly degraded to moderate turbulence and then we encountered a violent shear and jolt of severe turbulence. We were instantly rocked up 200 feet above our assigned altitude. The aircraft was attempting to climb. I countered the climb with forward stick pushing the stick momentarily to the forward stop. The aircraft was also in an un commanded slight left bank. I countered with nearly full right aileron. The aircraft did not respond to my control inputs for a second or two and continued to climb and bank left even though the nose was pointed down and I was at nearly full right stick deflection. After a short time the aircraft responded to my control inputs but was still being heavily buffeted by very strong turbulence for a short time before we retuned to controlled flight. Our flight attendants reported that they were slammed into their seats and pushed up into their seat belts as the aircraft oscillated between negative and positive G. Fortunately we had briefed the possibility of turbulence during our preflight briefing and all of the flight attendants and passengers were seated and wearing their seat belts. There were no injuries reported. I filed the required ELB report and reported the event to Dispatch. At the time of the event I was maintaining 250 Kts due to the turbulence. The severe turbulence event lasted possibly 5 seconds at its highest intensity the heavy turbulence that was very strong moderate or possible severe lasted approximately 20 seconds.