Good muesli is good, said Phil in comments a couple of days ago.
I’m sorry, I’m in Switzerland so this is probably sacriligeous, but Australians make much better bircher than the Swiss, at least in Geneva. It’s like the porridge. Australians restaurants have a respect for breakfast which is simply far and above how it is treated anywhere else. I’ve gotten tired of being disappointed by the stuff here when I go out for breakfast and decided I had to start making it myself.
I think ratio of oats to soaking liquid is a personal taste thing. At a minimum 1 applejuice to 2 oats, soaked overnight in fridge. I have also made it more like 1:1.
Yoghurt: Swiss yoghurt is dreadful runny stuff. To fix the local product you simply drain it to taste. You can use a coffee filter but if you have muslin/cheesecloth, so much the better (2 layers of muslin will do fine) overnight and it reduces by about 50% to almost soft cheese consistency. You may or may not wish to add honey. If you can get it, Greek yoghurt is not as tart as normal yoghurt. By draining ordinary yoghurt as suggested here, the liquid you discard is the whey, which is the thing that particularly gives the tartness you may not wish at breakfast.
Next day to assemble:
Mix a serving – always start off with a couple of tablespoons of previously prepared oats per serve with yoghurt and grated apple, I use one per two serves. Then add to taste fruit.
Variation one: poached pears, blueberries, toasted almond flakes/slivers. Good in winter when the variety of summer fruit is lacking.
Variation two: raspberries with passionfruit.
Variation three: anything with passionfruit. Anything good. Mango is terrific.
Poached pears: bring water flavoured with sugar and maybe cinammon stick, cloves to the boil. Add pears, reduce heat to low simmer. I gather pears discolour unless completely immersed, I covered with a round of baking paper. Left for about 15 mintes (when knife through them has no give, then ready), let cool in pan and stored in fridge in the cooking liquid.