Preheat your oven to 350°F (175°C) and grease a 9-inch round cake pan.
In a large bowl, whisk together the gluten-free flour, sugar, cocoa powder, baking soda, and salt.
Add the milk, vegetable oil, eggs, and vanilla extract. Mix until smooth.
Carefully stir in the boiling water (the batter will be thin, this is normal!).
Pour the batter into the prepared cake pan.
Bake for 30-35 minutes, or until a toothpick inserted in the center comes out clean.
Let the cake cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.
