Preheat the oven to 180 °C (356°F) .
Using a saucepan at low heat, melt the butter and dark chocolate together. Once the chocolate is melted, remove the saucepan from the heat.
Next, add in the brown sugar, granulated sugar and mix together using a whisk.
Afterward, let the saucepan cool down to room temperature before adding the eggs, coffee, and vanilla extract. Whisk all the ingredients together until combined.
In a separate bowl, whisk the flour, xanthan gum, salt, cocoa powder together. Then add the wet ingredients to the dry ingredients and mix them together using a spatula.
Align a square pan with baking paper before adding in the batter. Level the batter in the square pan using a spatula.
Bake the brownies at 180 °C (356°F) for 27-30 minutes or until the edges are firm.