Shortbread is perfect as-is, but can also be customized however you like it; flavour the dough with citrus zest, tea, lavender, spices or extracts, and try stirring in finely chopped dark chocolate or toasted nuts, or anything else you can think of.
Preheat oven to 350°F.
In a medium bowl, beat the butter, sugar, citrus zest, tea or lavender (if you're using it) and vanilla until pale and creamy.
Add the flour and salt and beat on low or stir by hand until you have a soft dough.
Press the dough into an ungreased 8 or 9-inch round pan and poke a few times with a fork, then press down around the edges with the tines of a fork.
Bake for 12-15 minutes, or until pale golden.
Cool for a few minutes, but slice while still warm.