Preheat the oven to 180°C (350°F) and line an 8"x8" baking pan with baking paper.
Melt the butter and mix with the brown sugar and sugar.
Hand whisk in the egg and vanilla extract.
Add in the gluten free flour, baking soda and cocoa and mix until all combined.
Stir in the chocolate chips if you are adding them.
Pour into the prepared pan.
Sprinkle over the white chocolate buttons to create a polka dot effect.
Place in the oven for 20-25 minutes. The sides and top will be set but the middle will wobble slightly. (If you don't want them slightly under baked, wait until the middle doesn't wobble at all.