Beat butter, sugar and vanilla until light and fluffy. Sift flour with baking soda and salt. Add to butter mixture to make a soft dough. Refrigerate 30 minutes. Turn out dough onto a lightly floured surface. Divide in half. Shape each half into a roll 8 inches long (about 2 inches in diameter). Wrap in waxed paper and refigerate several hours or overnight. Preheat oven to 375 degrees F. Slice the roll thinly (about 1/4 inch). Place on an ungreased cookie sheet 1 inch apart. Bake 8 - 10 minutes (watch carefully - don't want them too brown on the bottom - you'll have to experiment with your oven to get the time right). Allow cookies to cool on the cookie sheet for a few minutes before removing from the sheet to a wire rack. Store in an airtight container if they last long enough to store (I know they don't last long at my house).