Creating this delightful Gluten Free Cinnamon Coffee Cake is simple if you follow these steps:

1. Preheat the Oven: Preheat your oven to 350°F (175°C). Grease and flour a 9-inch round cake pan.
2. Mix Dry Ingredients: In a large bowl, whisk together the gluten-free flour, granulated sugar, brown sugar, baking powder, baking soda, salt, and ground cinnamon.
3. Prepare Wet Ingredients: In another bowl, cream the softened butter until smooth. Add the eggs one at a time, blending well. Stir in the sour cream and vanilla extract until well combined.
4. Combine Mixtures: Gradually add the wet ingredients to the dry ingredients, mixing until fully incorporated and smooth.
5. Prepare Cinnamon Swirl: In a small bowl, mix together ⅓ cup brown sugar and 1 tablespoon cinnamon. Set aside.
6. Layer the Batter: Pour half of the batter into the prepared cake pan. Spread it evenly. Sprinkle half of the cinnamon mixture over the batter.
7. Add Remaining Batter: Pour the remaining batter into the pan and evenly spread it on top. Lastly, sprinkle the rest of the cinnamon mixture over the top surface.
8. Prepare Crumble Topping: In a separate bowl, mix rolled oats, gluten-free flour, brown sugar, and melted butter. Combine until crumbly. Sprinkle this topping over the cake batter.
9. Bake: Place the cake in the preheated oven and bake for 35–40 minutes or until a toothpick comes out clean from the center.
10. Cool: Once baked, remove the cake from the oven and allow it to cool in the pan for about 10 minutes before transferring it to a wire rack.