Andy, the Wales Outdoors owner has been backcountry backpacking since his schooldays. Back then it was heavy kit shared amongst school mates and relatively heavy, fresh food but utilising some dried ingredients such as dried apple chunks and vesta meals.
Things have moved on. Andy's meals of choice for a couple of days on the hill are Mountain Trails veggie freeze dried ration packs. Well formulated and actually quite delicious and NO washing up :)
For any longer Andy would want to include some home made meals that included some fresh ingredients. However, in the UK it is rare to be on the hill for multiple days without coming across a road a so a shop or two. Perhaps in Scotland this can be the case.
Mountain walking with all you need to survive is hard work. It's possible that for multiple day trips 4500 calories or more are needed and this is a difficult ask. Most go for cheese or chocolate to get those calories in. Or, you can have a slap up meal at the end of the trek :)