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.
In a medium bowl, whisk together the gluten free baking flour, almond flour, baking powder, baking soda, and salt. Set aside.
In a large bowl, beat the softened butter and granulated sugar with an electric mixer until very light and fluffy, about 4 minutes. This extra creaming creates that signature sugar cookie texture. Beat in the eggs one at a time, then mix in the lemon juice, lemon zest, vanilla extract, almond extract, and sour cream until smooth.
Fold the dry ingredients into the wet ingredients with a spatula until just combined. The batter will be thick and smell incredible, like sugar cookie dough with a bright lemon twist.
Pour the batter into the prepared pan and smooth the top. Bake for 50 to 58 minutes, until golden on top and a toothpick inserted in the center comes out clean or with a few moist crumbs.
Let the bread cool in the pan for 15 minutes, then lift it out and transfer to a wire rack to cool completely.
Once the bread is fully cool, whisk together the powdered sugar, lemon juice, and lemon zest until you have a thick but pourable glaze. Drizzle it over the top of the bread, letting it cascade down the sides. Let the glaze set for 10 minutes before slicing.