Preheat the oven to 300°F. Lightly grease one 9-inch round or 8-inch square pan.

Beat the softened butter and sugar until light and fluffy, then mix in the vanilla.

Gradually add the flour and salt, stirring until a crumbly dough forms.

Press the dough evenly into the prepared pan and prick it all over with a fork.

Bake for 35 to 40 minutes, until lightly golden.

Cool in the pan for 10 minutes, then cut into wedges or squares while still warm.