Preheat the oven to 375 F and grease a 9x5 inch loaf pan.
In a large bowl, whisk together the gluten free flour, tapioca starch, sugar, baking powder, and salt until well combined.
Pour in the entire bottle of gluten free beer and the melted butter. Stir with a wooden spoon until just combined. The batter will be thick, sticky, and slightly bubbly from the beer. Do not overmix.
Scrape the batter into the prepared loaf pan and smooth the top with a wet spatula. Drizzle the remaining 2 tablespoons of melted butter evenly over the top. Sprinkle with a pinch of flaky sea salt.
Bake for 45 to 55 minutes, until the top is deep golden brown, the edges are set, and a toothpick inserted into the center comes out clean.
Let the bread cool in the pan for 10 minutes, then turn out onto a wire rack. This bread is best served warm, sliced thick with salted butter. It has a wonderfully tender crumb with a slightly crispy, buttery crust.