I never know what the difference is between cottage pie and shepherd's pie! Is it to do with using beef rather than lamb? Or is it about sliced potato on top vs mashed potato?
Here's how I make my whateverit's called!
fry a large, diced onion till soft
peel and slice 3 or 4 carrots and add to the onions
add 400-500g mince (beef) and fry till brown, breaking it up with a wooden spoon as it browns
season with salt and black pepper and any dried herbs you like/have to hand
add one Oxo cube and then pour enough water on to cover
Sloosh of Worcestershire sauce and a bit of soy sauce
cook, covered, for at least half an hour
take off lid and cook until liquid is reduced and it's not too wet
make mashed potato as usual, but don't make it too wet
pour mince into an oven dish, spread mash on the top and bake until nicely browned
Hope this helps!
(By the way, it's probably nicer if you make it on day one and cook it on day two - flavours will have deepened/matured)