The Brits and Aussies call it "Cottage Pie."
Why "Shepherd's"? Because it is traditionally made with ground lamb or mutton. That's how Alton Brown makes it.
Americans use ground beef, usually. Ground mutton is not a typical supermarket item. Go ahead and use instant mashed potato if you must - the recipe don't care.
I am hoping some Mom will try each of the recipes in this series, and report back on family response.