1 teaspoon vanilla (more if you're into that sort of thing!)
2 cups plain flour
1/4 teaspoon baking powder
1 pinch salt
Cream butter and sugar.
Add egg, then vanilla.
Stir the baking powder into the flour, then add to the egg/sugar/butter mix with the salt.
Stir until it all comes together, and pat into a flat disc. Put it on a plate with a tea towel covering, and put it in the fridge for 30 minutes or so, until fairly firm - you want it to roll without being sticky and soft, but also not too hard.
Roll fairly thin (about half a centimetre is usually more than enough) and cut into shapes. Place on cookie trays
Bake at 160-180C for 10-15 minutes, checking after 10. You don't want them to brown too much on the edges (or all the way through if they're super-thin).