Place box/bench behind you at desired squat depth.

Set bar on upper back (powerlifting style).

Unrack bar, step back, assume squat stance (shoulder-width or wider).

Push hips back, bend knees, lower onto box.

Keep shins vertical, back straight.

Sit fully on box briefly (relax hip flexors, don't bounce).

Drive through heels, chest up, return to start.

Repeat.