Pour the mixture into a medium bowl. Let cool for about three minutes. Stir in eggs until smooth. (Add vanilla now, if using) Add gluten-free flour, cocoa powder, and salt. Mix until smooth. Stir in nuts or chocolate chips if using.
Spread batter into prepared pan.
Bake for about 30 minutes. Or until a toothpick inserted comes out clean or with just a few crumbs on it.
Cover brownies and store on the counter for up to four days.
To freeze: Wrap cooled brownies or place into a freezer container. Freeze up to three months.
For Gluten-Free and Dairy-Free Brownies: Replace the butter with a dairy-free butter replacement. Use dairy-free chocolate.