Preheat your oven to 350°F (175°C) and grease a 9-inch round cake pan with unsalted butter or non-stick spray.

In a large mixing bowl, whisk together gluten-free all-purpose flour, baking powder, baking soda, salt, and cinnamon until fluffy.

In another bowl, whisk together melted butter, granulated sugar, brown sugar, eggs, and vanilla extract until smooth.

Gradually pour the dry ingredients into the wet mixture, stirring gently until just combined.

Fold in the diced apples until evenly distributed.

Pour the batter into the prepared cake pan and smooth the top. Bake for 30-35 minutes.

While the cake cools on a wire rack, mix powdered sugar and milk to make the glaze.

Once cooled, drizzle the glaze over the cake.