Preheat the oven to 350°F. Line an 8.5 x 4.5 inch loaf pan with parchment paper, leaving some overhang for easy lifting.
Blend the cottage cheese, eggs, melted butter, 2 tbsp lemon juice, lemon zest and vanilla extract in a blender until completely smooth.
In a large bowl, whisk together the almond flour, coconut flour, granulated sweetener, baking powder and sea salt. Pour in the blended mixture and stir until a thick, smooth batter forms.
Gently fold in the blueberries, saving a small handful for the top. Spread the batter into the prepared pan and press the reserved blueberries into the surface.
Bake for 55 to 60 minutes, until the top is golden and a toothpick inserted in the center comes out clean. Tent the pan loosely with foil after 35 minutes to prevent over-browning.
Cool the bread in the pan for 15 minutes, then lift it out and cool completely on a wire rack.
Whisk the powdered sweetener with 4 tsp lemon juice until smooth and pourable. Drizzle the glaze over the cooled bread and let it set for 10 minutes before slicing.