Preheat oven to 375°. In bowl, whisk flour and baking soda. In large bowl, beat sugar and butter until creamy, about 2 minutes. Beat in egg and vanilla, then flour mixture. Stir in pecans. Place tablespoonfuls of dough on 2 parchment-lined baking sheets, spacing 1 1/2 inches apart. Bake until golden brown, about 12 minutes. Cool on sheets on racks.