Preheat oven to 350 degrees F convection or 375 degrees F. for regular oven. If using Cup4Cup, use 350 degrees F.
In a large mixing bowl, beat the softened butter or margarine and both sugars until creamy. Add egg and beat just until blended, scraping side of the bowl often. Beat in vanilla and baking soda.
Add the flour and stir by hand or using the lowest speed of a mixer until blended.
Drop mixture by heaping tablespoonfuls (or use a medium size cookie scoop), spacing 2 inches apart, on ungreased baking sheets. Bake one sheet at a time for 10-12 minutes or until edges are golden. Remove cookies to wire racks and cool completely.
For even better cookies, scoop cookie dough onto a plate lined with plastic wrap, cover and chill overnight. Bake cookies as directed above. I usually bake a few right away, then chill the rest of the dough and bake a few every day.