Preheat the oven:
Preheat your oven to 350°F (175°C). Line baking sheets with parchment paper or silicone baking mats.
Cream the butter and sugar:
In a large mixing bowl, use an electric mixer to beat the softened butter and brown sugar together until light and fluffy (about 2-3 minutes).
Add wet ingredients:
Beat in the egg and vanilla extract until well combined.
Mix dry ingredients:
In a separate bowl, whisk together the flour, baking soda, salt, and cinnamon (if using). Gradually add the dry ingredients to the wet mixture, mixing just until combined. Avoid overmixing.
Shape the cookies:
Scoop tablespoon-sized portions of dough and roll them into balls. Place the dough balls about 2 inches apart on the prepared baking sheets.
Bake the cookies:
Bake for 8-10 minutes, or until the edges are set and the centers look slightly underbaked (they will continue to firm up as they cool).
Cool the cookies:
Let the cookies cool on the baking sheet for 5 minutes, then transfer them to a wire rack to cool completely.