Blend together butter, sugar, vanilla and salt in a bowl with a fork until mixture forms soft dough. Crimp edges decoratively and prick dough allover with tines of a fork. Score dough crosswise with the back of a knife into 8 sections. If desired, sprinkle with chopped toasted nuts and press gently into dough with your fingertips. Bake shortbread in middle of oven until edges are golden, about 15 minutes.
Transfer slices with a spatula to rack to cool completely.
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