In a large bowl whisk together eggs, milk and beer. Gradually whisk in flour. Add the salt and oil then whisk the batter vigorously for 3 to 5 minutes, so all is thoroughly incorporated. Let the batter sit for 1 hour.
Heat a large non-stick frypan over medium heat. Brush it with butter and when it's hot but not smoking pour a 1/3 cup of batter into the centre of the frypan and rotate it so the batter covers the bottom of the pan in a thin layer pouring out any excess batter.
Cook the crepe until it is just golden on one side; 1 to 2 minutes then turn it and cook until it is golden on the other side; about 30 seconds.
Transfer to a plate and keep warm by covering with aluminium foil. Continue until all of the batter is used.