Ahh autumn, I know Keats was fond of you, I am too, for different reasons though. Autumn means that the oven can be used with impunity & that stews are back on the menu, Steak & ale pie means both.
You'll need some shortcrust pastry, which you can make or buy. Steak (one of the cheaper cuts, its is about to be cooked for several hours) onions, mushrooms and Beer. Beer is an important ingredient in this dish, in fact it's almost all the stock/gravy so choose well. Ideally it'll be a fairly dark strong beer to go with the deep flavour of the beef (you could use lamb and a lighter ale if you like). I went with Theakstons "Old Peculiar" which I've always been fond of. So get you best stewing/casseroling pan out and melt some butter, season it as you like. Chop some onion and sweat it in the butter. Add a mushroom or 3 (these will probably melt into the stock, they are there to add body). Toss your steak in flour and brown it in the oniony shroom butter. Pour in the beer (500ml/pint) add some herbs and simmer. You have an hour or 3 to amuse yourself, stop simmering when the stock, gravy is just a touch less thick than you'd like.
Line a greased pie plate with pastry, and slice a couple more mushrooms. Stir the mushrooms into the steak stew & then ladle the lot into the pastry lined plate. Make a pastry lid, attach it & brush with milk. Into the oven on gas 4 for 30-40 mins. Enjoy.
If you can't eat the pie in one sitting, you can either eat it cold later or like the one above put it in a low oven to heat through whilst you cook some spuds & some veg.
Make this, if nothing else it'll make your kitchen smell awesome. Cheat & buy the pastry. Cheat more and use an ovenproof pan & just lay the pastry over the top of it. Just make the pie, its the thing now the nights are drawing in.