Rinse chicken and cavity under running water. Pat skin dry with paper towel. Remove parson's nose if you want.
Rub salt over skin, paying attention to wings and legs, wherever you want the skin to be crispy. Probably ends up being about 2-3 teaspoons of salt. If I just left the skin treatment at salt (and herbs) and placed in fridge, this would be a dry brine.
Using a finger carefully pry open the cavity between the skin and breast meat on each side and slide in sliced butter and choice of fresh herbs. Cavity does not need to be filled. The butter helps to keep breast moist. Parsley, thyme always work nicely.
Put lemon and more fresh herbs into cavity and secure skin with a toothpick or similar.
Baste the chicken all over with soy sauce. Don't worry if it's a bit patchy, as long as all the skin gets a little soy. However, you don't want little rivers of soy as those marks will remain, so ensure all areas get covered.
Sprinkle with dried herbs of choice and pepper.
Place on top of sliced onion on baking paper in baking tray. Leave uncovered or place cling wrap very loosely over top and marinade in fridge for several hours at least.
Take chicken of the fridge 20 minutes before cooking. Re-baste with any soy that has dripped off. Drizzle with a little extra virgin olive oil. Preheat oven to 220℃/428℉.
Cook in middle of oven for 20 minutes on 220℃/428℉, then turn down oven to 210℃ /392℉ for remainder of roasting time (ie 40 minutes per kilogram plus 10-15 minutes) so another 1 hour and 15 minutes for a 2 kg chicken.
Halfway through, check how much fat has dripped from the chicken. You can siphon some of this off, retaining some of the pan juices for basting, or change the baking paper. Baste the skin. Rearrange any onion that has shifted.
To test if cooked put a skewer into thickest part and see if juices run clear. Otherwise use thermometer (I've never used one, I'd rather than slice a little into the breast meat to check, because who cares if it's not completely intact. If the breast's white, you're clear). Some people say to rest the chicken but I've never bothered. By the time I organise myself to carve is rest enough.
Serve with a little drizzle of the pan juices.