Heat oven to 375° F. Line two baking sheets with parchment paper or aluminum foil.
With an electric mixer on medium-high, beat the butter, brown and granulated sugars, corn syrup, and vanilla for 3 minutes. Add the egg and beat until combined.
In a separate bowl, whisk together the flour, salt, and baking soda. Reduce mixer speed to low and slowly add the flour mixture to the egg mixture. Add ingredients from the variation of your choice.
Unless the directions for the variation state otherwise, form the dough into tablespoon-size mounds. Place on the prepared baking sheets, 2 inches apart. Bake until lightly browned at the edges, 12 to 15 minutes. Cool on the baking sheets for 5 minutes. Transfer the cookies to wire racks. Cool completely.
To Make Now and Bake Later: When you mix a batch of cookies, double the recipe. Bake half the dough according to the recipe and divide the rest into 4 equal portions. Roll each portion into a log about 1 1/2 inches in diameter. Wrap each log in plastic, then place in a resealable plastic bag. To save yourself time and hassle, label the bag with the flavor, the oven temperature, and the baking time, adding 3 to 6 minutes to the regular oven time. Freeze the dough for up to 3 months. To bake, slice the frozen dough into rounds about 1/2 inch thick, making as few or as many as you would like. Bake on a parchment- or foil-lined baking sheet.