Preheat oven to 300°F (150°C).
In a large bowl, beat the softened butter and sugar together until light and fluffy, about 2-3 minutes.
Add the flour, cornstarch, and salt and mix until a dough forms.
Press the dough into an ungreased 9-inch round baking pan or 8-inch square baking pan and use a roller to flatten the surface and precut lines 7x5
Prick the dough all over with a fork all the way through.
Bake for 1 hour, until lightly golden brown.
Allow to cool in the pan for 10 minutes, then cut into wedges or squares while still warm.
