Make an x shaped slit on the top of the tomato with the tip of a small knife. Cut the green core out of the other end. Boil the kettle, put tomato in a bowl and cover with hot water. After a minute or so the skin will start to split. Run it under a cold tap to avoid the flesh going mushy, and peel skin off with sharp edge of knife.
Proceed with recipe of choice i.e. salsa. For tomato concasse, cut in half after skinning, scoop out the pips and cut flesh into small diamonds(or tiny Leaning Towers of Pisas, if you wish. Knock yourself out.)