Preheat your oven to 325°F / 165°C. Prepare a 9x5-inch loaf pan by lining it with parchment paper, leaving an overhang on the sides to act as handles for easy removal.
In a medium bowl, whisk together the dry : coconut flour, granular erythritol, baking powder, xanthan gum, and salt to break up any clumps.
In a separate large bowl, whisk the eggs until light and frothy.
Add the sour cream, avocado oil, and vanilla extract, and whisk until the mixture is smooth and fully combined.
Gradually pour the dry into the wet , stirring with a spatula until just combined.
Do not overmix. Gently fold in the poppy seeds, lemon zest, and fresh lemon juice.
Pour the batter into the prepared loaf pan and smooth the top with your spatula.
Bake for 50-60 minutes, or until the top is golden brown and a toothpick inserted into the center comes out clean.
While the loaf bakes, prepare the glaze.
In a small bowl, whisk the heavy whipping cream and confectioners'-style erythritol until smooth and the sweetener has completely dissolved.
Set aside.
Remove the loaf from the oven and let it cool in the pan for 15 minutes.
Pour the glaze evenly over the warm loaf. Allow the loaf to cool completely in the pan before using the parchment handles to lift it out, slice, and serve.
