• Gather the ingredients.
• Spray an 8" x 8" baking pan with non-stick cooking spray. Next, fold a 16" length of Parchment Paper to a width of 7" and fit it into the baking pan, so that the excess hangs over the edges for easy removal of the cake. Set aside.

Making the topping:

• In a small sauce pan, melt the butter over low heat. Once completely melted, remove from heat and let cool slightly.
• Using a whisk, mix in the sugars, salt, cinnamon and egg yolk to the melted butter, thoroughly mixing.
• Add the GF Flour to the butter mixture, blending well. The mixture will look like ground meat. Set aside.
  

Making the Cake:

• Place one of your oven racks in the upper-middle position of the oven and preheat oven to 325 degrees.
• In a stand mixer, using the paddle attachment, mix the GF Flour, Granulated Sugar, Salt, Xanthan Gum (if needed) and Baking Soda on low until completely blended.
• Next, add the Butter to the flour mixture, one piece at a time, mixing on low until butter pieces are no longer visible - mixture will resemble coarse sand.
• Add the Sour Cream, Eggs, Yolk and Vanilla to the Flour mixture and mix on medium-high until batter is light and fluffy.

Putting it Together:

• Scrape the batter into the prepared baking pan and smooth the top.
  
• Using your hands, break the Topping Mixture into large pea-sized pieces and sprinkle over the top of the batter to completely cover.
  
• Bake for 35-45 minutes, rotating the pan halfway through baking. It's done when the middle is no longer jiggly and a wooden toothpick inserted into the middle comes out clean.
  
• Let cool in the pan for 30 minutes before removing, using the excess Parchment Paper to lift and pull the cake out.
• Place on a platter or cutting board to cut and serve. Enjoy!