The missing 'recipe': Thermal conduction 'revealed' starting from the foundations

It's a bit like the difference between preparing a dish following a recipe detailing ingredients and procedure, or trying to do it just by looking at photos of the dish: in many cases good results can also be obtained with the second method but, clearly, knowing the recipe not only guarantees a successful outcome but also allows us to devise variants of the dish, using different and perhaps even tastier ingredients. This also happens in the world of physics, where in some cases the "recipe" is c...