Preheat the Oven: Preheat your oven to 350°F (175°C). Spray a 9×13-inch cake pan with nonstick baking spray.
Prepare the Cake Batter:
In a large bowl, whisk together the gluten-free flour, baking powder, sugar, ground cinnamon, and salt.
In a separate bowl, mix the vegetable oil, eggs, vanilla extract, and milk until smooth.
Pour the wet ingredients into the dry ingredients, stirring until smooth.
Set aside ½ cup of the cake batter for the cinnamon filling, then pour the remaining batter into the prepared cake pan.
Make the Cinnamon Filling: In a small bowl, combine the reserved ½ cup of cake batter with the brown sugar, ground cinnamon, and melted butter. Mix until smooth.
Create the Swirl: Drop spoonfuls of the cinnamon filling mixture over the top of the cake batter. Use a butter knife to swirl the filling into the batter, creating a marbled effect.
Bake the Cake: Bake for 35-40 minutes or until a toothpick inserted into the center comes out clean.
Prepare the Glaze: In a mixing bowl, combine the powdered sugar and 5-6 tablespoons of milk, mixing until smooth.
Glaze the Cake: Pour the glaze over the warm cake, gently spreading it with a spatula.
Serve: This cake can be served warm or cold. Enjoy!
