Preheat your oven to 350F. Line a cookie sheet with parchment paper or a silicone mat.
In a large bowl, combine softened unsalted butter, brown sugar, and white sugar. Use a spatula to mix until smooth.
Then, add in the egg and vanilla extract. Stir until everything is well combined.
Add the all-purpose flour, baking soda and salt. Stir until the mixture forms cookie dough.
Fold in the crushed Twix chocolate bars, making sure to leave some bigger pieces for a nice texture.
Use a cookie scoop or your hands to form cookie dough balls. Place them on the prepared baking sheet, leaving space between each cookie.
Place the cookie sheet in the oven and bake for about 8-10 minutes. Keep an eye on them until the tops of the cookies are golden brown.
Once baked, remove the cookies from the oven and let them sit on the baking sheet for a few minutes. Then, transfer them to a wire rack to cool completely.