Line a 13- x 9-inch baking pan (glass).
To create a double boiler, set a medium metal or heat-safe glass bowl over a small saucepan of simmering water.
Melt butter in a bowl. Once melted, add dark chocolate and cook. Stir occasionally until melted and smooth, about 10 minutes. Remove from heat.
Crack eggs in a large bowl. Then, whisk together granulated sugar, light brown sugar, cocoa powder, vanilla, salt, and espresso coffee granules in the bowl with the eggs until smooth. Gently whisk in chocolate ganache mixture until smooth. Fold in coconut flour until combined. It may help to gently press any lumps that you see as you mix the brownie batter.
Transfer mixture to a prepared baking sheet by spreading batter in an even layer. Refrigerate for 1 hour.