In a small saucepan, melt the butter over medium heat. Continue cooking, swirling the pan occasionally, until it turns deep golden amber and smells nutty, about 5 to 7 minutes. Pour it into a large heatproof bowl and let it cool for about 10 minutes.
While the butter cools, preheat your oven to 350°F (175°C). Grease a 9x5 inch loaf pan and line it with parchment paper. In a medium bowl, whisk together the gluten free baking flour, almond flour, baking powder, baking soda, salt, and cinnamon.
To the cooled brown butter, add the dark brown sugar and whisk vigorously until combined and slightly thick. Add the eggs one at a time, whisking well after each, then stir in the vanilla extract and sour cream.
Fold the dry ingredients into the wet ingredients with a spatula until just combined. Fold in 3/4 cup of the chopped toasted pecans, reserving the rest for the top.
Pour the batter into the prepared pan. Scatter the remaining pecans over the top and press them in gently. Sprinkle the turbinado sugar over everything for a crackly cookie-like crust.
Bake for 50 to 60 minutes, until the top is deeply golden and a toothpick inserted in the center comes out with just a few moist crumbs. Let the bread cool in the pan for 15 minutes before removing to a wire rack to cool further.