�knob� is a British term meaning more or less a couple of tablespoons of butter - it is purposefully meant to be vague to encourage the creator of the recipe to cook till a personalized taste is reached through the butter.
The terms flammable and inflammable do mean the same, the terms are just used for different things.
Flammable is used for chemicals etc, and inflammable is normally used for materials i.e. cloth etc.