Preheat oven to 375°F (190°C) and grease a 9x5-inch loaf pan.
In a large bowl, whisk together the gluten-free flour, baking powder, and salt.
In a separate bowl, whisk the melted butter, sugar, warm milk, eggs, and apple cider vinegar until smooth.
Pour the wet ingredients into the dry ingredients and mix with a spatula until a thick, sticky batter forms.
Transfer the batter to the prepared loaf pan and smooth the top with a wet spatula.
Bake for 45-50 minutes, or until a toothpick inserted in the center comes out clean.
Let the bread cool in the pan for 10 minutes, then transfer to a wire rack to cool completely before slicing.