Preheat your oven to 350°F (175°C). Grease a 9x5 inch loaf pan and line it with parchment paper, leaving an overhang on the long sides for easy removal.
In a small saucepan, melt the 1/2 cup of butter over medium heat. Continue cooking, swirling occasionally, until the butter turns golden amber and smells nutty, about 5 to 7 minutes. Pour the brown butter into a large bowl and let it cool for 10 minutes.
In a medium bowl, whisk together the gluten free baking flour, almond flour, baking powder, baking soda, salt, and 1 tablespoon of cinnamon. Set aside.
To the cooled brown butter, add the granulated sugar and brown sugar. Whisk until well combined. Add the eggs one at a time, whisking after each, then stir in the vanilla extract and sour cream until smooth.
Fold the dry ingredients into the wet ingredients with a spatula, stirring just until no dry streaks remain. The batter will be thick and luscious.
In a small bowl, mix together the 1/4 cup sugar, 1 tablespoon cinnamon, and melted butter for the swirl. Pour half the batter into the prepared pan, dollop the cinnamon sugar swirl mixture on top, then add the remaining batter. Use a toothpick or skewer to create gentle swirls through the layers.
In a tiny bowl, mix the 2 tablespoons sugar and 1 teaspoon cinnamon for the crust. Sprinkle this evenly over the top of the batter.
Bake for 50 to 60 minutes, until a toothpick inserted in the center comes out with just a few moist crumbs. Let the bread cool in the pan for 15 minutes, then lift it out using the parchment overhang and cool on a wire rack.