01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - Whisk together gluten-free flour, baking soda, and salt in a medium bowl. Set aside.
03 - Beat butter, brown sugar, and granulated sugar until light and fluffy, about 2-3 minutes.
04 - Mix egg and vanilla extract into butter mixture until well combined.
05 - Gradually add dry ingredients to wet mixture, mixing until just incorporated.
06 - Fold in dark chocolate chips, toffee bits, and nuts if using.
07 - Scoop tablespoon-sized portions onto prepared baking sheets, spacing 2 inches apart.
08 - Bake for 10-12 minutes until edges are golden and centers look just set.
09 - Cool on baking sheet for 5 minutes before transferring to wire rack to cool completely.