Instructions
Begin with the bar racked at or just above knee height. Add weight to just one side of the barbell. Place yourself in front of the bar, with your feet directly under it. Have your feet approximately hip width apart and grab hold of the bar with a double overhand grip. Lift the bar off the rack, and move back a step in to position.
Slowly lower the weight with a bend in your knees, bending at the hips and keeping your core braced. Lower the bar until you feel a slight stretch in your hamstrings - usually when the weight is halfway between your knees and your ankles - then drive your hips forwards and use your hamstrings and glutes to power back up to standing. You should find that with the uneven weight you have to work harder to stabilise the bar.
Repeat for desired number of repetitions. Then change the weight to the other side and repeat.
Tips
Not much weight needs to be added to one side of the bar to make this exercise effective.