Basic cottage pie is really easy
heat some oil in a pan, add chopped onions and cook them until softened, add the mince, squeeze of tomato puree, sprinkling of mixed herbs, salt and pepper and some worcestershire sauce, stir it well and continue to cook until the mince browns, add some beef stock and simmer for about 30-40 mins, at this stage if you think the gravy in it needs thickening add some gravy granules and stir them in well.
Put it into a pie dish, top with mash and either put it under the grill or in the oven til the top goes brown.
I tend to put hidden veg in mine, not for kiddies but for me, hate the taste of veg so if I chop it small I can eat it without tasting it
you can also bulk it out with red lentils, put a handfull in with the beef stock (you may need to simmer it for longer though) it bulks it out and you can't taste them but it makes the mince go a lot further so saving you dosh also cottage or shepherd pie freezes well.