Preheat the oven to 180C / 356F and line a 12 cup muffin tin with paper or silicone liners.
In a large mixing bowl, combine almond flour, baking powder, xylitol and poppyseeds.
In a separate smaller bowl, whisk together the eggs, sour cream, vanilla extract, lemon zest and juice until evenly combined.
Mix the wet ingredients with the dry and fold together gently until just combined.
Pour into the prepared muffin tin and bake for 20 - 25 minutes until the tops are golden and a toothpick comes out clean. Leave to cool while preparing the frosting.
To make the frosting, using a hand beater or stand mix, whip the butter, cream cheese and lemon, saving 1 tablespoon of rind for serving.
Whip in the powdered xylitol until completely incorporated.
Once the muffins are cool, pipe or spread the frosting on top and finish with reserved lemon rind and a few extra poppy seeds for added crunch.