Fudgy Peanut Butter Swirl Brownies (Gluten Free)

unsalted butter

dark chocolate, chopped ((I've used 70% dark chocolate, but anything above 60% will work well))

caster sugar ((you can use granulated sugar, but caster sugar is recommended))

medium eggs, room temperature

plain gluten free flour blend ((I've used Doves Farm Freee plain gluten free flour blend, which doesn't contain xanthan gum))

xanthan gum ((omit if your GF flour mix already contains xanthan))

cocoa powder

salt

natural unsweetened smooth peanut butter