Preheat your oven to 350°F (177°C) and line an 8x8-inch (20x20-cm) baking pan with parchment paper.
In a small saucepan over low heat, melt the dairy-free butter alternative and sugar together, stirring occasionally, until smooth and glossy. Remove from the heat and let it cool slightly.
In a large bowl, whisk the eggs and vanilla extract until well combined. Add the butter-sugar mixture and whisk again until smooth.
In a medium bowl, whisk together the gluten-free flour, cocoa powder, and salt. Add the dry ingredients to the wet ingredients and stir with a wooden spoon or a spatula until well incorporated. Fold in the dairy-free chocolate chips and any optional mix-ins.
Pour the batter into the prepared pan and spread it evenly with a spatula. Bake for 25 to 30 minutes or until a toothpick inserted in the center comes out with a few moist crumbs attached.
Let the brownies cool completely in the pan on a wire rack before cutting into squares and enjoying.