Should I use just enough boiling water from the kettle to cover them (less water to bring back to the boil) or fill the saucepan right up (more water, but it won't have been cooled as much by the peas)
IMO to keep maximum crunch you want a lot of water, rolling boil, dump the frozen peas in, temp up and cover, as soon as the water wants to boil over they're done. If peas weren't frozen then don't turn up the heat and don't cover. Once done pour out in to collinder and rinse with cold water
Frozen peas:
Should I use just enough boiling water from the kettle to cover them (less water to bring back to the boil) or fill the saucepan right up (more water, but it won't have been cooled as much by the peas)