Preheat your oven to 325 degrees F. Grease a 9x5-inch loaf pan and line the bottom with parchment paper. In a large bowl, whisk together the almond flour, granulated erythritol, and baking powder.
Add the eggs, melted butter, sour cream, 2 tablespoons lemon juice, 1 tablespoon lemon zest, and vanilla extract. Stir with a spatula until a smooth, thick batter forms with no dry spots.
In a small bowl, toss the fresh blueberries with 1 teaspoon of almond flour from the pantry. This light coating helps prevent the berries from sinking to the bottom during baking. Gently fold the coated blueberries into the batter.
Pour the batter into the prepared loaf pan and smooth the top evenly. Bake for 50 to 55 minutes, until the top is deep golden and a toothpick inserted in the center comes out clean or with just a few moist crumbs.
If the top begins to brown too quickly during baking, loosely tent it with a piece of foil for the remaining time. Let the cake cool in the pan for 15 minutes, then carefully turn it out onto a wire rack to cool completely. The cake slices much cleaner when fully cooled.
While the cake cools, whisk together the powdered erythritol and 1 tablespoon lemon juice until smooth. The glaze should be thick but pourable. If it is too thick, add a tiny splash more lemon juice.
Drizzle the lemon glaze over the top of the cooled pound cake, letting it run naturally down the sides. Scatter the remaining lemon zest over the top. Allow the glaze to set for about 10 minutes before slicing and serving.
