My procedure is something like this, not the 'least amount of steps' but rather a slow, sure and safe way:
Frozen yeast, slant, 5ml, 20ml, 100ml, 500ml, 2L
The slant allows me to visually check the yeast viability after coming out of the freezer, then the small steps help 'proof' the yeast, keep any infection sources under control and hopefully get maximum growth and health from the yeast at each step.
In theory with sterile conditions/media you could go directly from the freezer to the 2L starter, or any number of intermediate steps, if the only criteria was 'least number of steps'. However, depending on what/where you read, steps of about 6-10x are usually recommended.