This evening my DiL made some sandwiches. The butter was spread as a thin film all the way out to the crusts.
My way is to dig out a knob and plonk it on the bread then give it a bit of a spread - repeat four or five times. There are thick bits, spreaded bits and even a few gaps with nothing. But when two slices are put together things even themselves out - sort of.
Yes, as Jan, really. The more important protocol, though, is to make sure any layer of peanut butter on top of the bread is a minimum of half an inch thick. And covering everything up to the sides.
In a complete non-sequitur, I'm currently experimenting with toasting pitta bread ......
Put the slice of bread or barm cake on the bread board. Take a knife and get some butter or similar spread on the knife and slowly spread it on the bread. I try to get and even covering. During the war when it was rationed my mother used to say but the butter round the edge and the filling in the centre. Anyone lifting the edge of a sandwich would assume the butter went all the way across the slice.