Pre-heat oven to 350*F.
In a bowl, whisk together the almond flour, coconut flour, lupin flour, baking powder, baking soda, xanthan gum and salt. Then set aside.
In another larger bowl, add the sour cream, melted butter, lemon zest, lemon juice, heavy cream and monkfruit sweetener. Whisk well to combine.
Add the eggs and vanilla extract and whisk again very well, until small bubbles can be seen at the top of the mixture.
Add the dry ingredients from before to the wet ingredients and then use a spoon to combine. Stir well until a thick dough has formed.
Add the blueberries and gently fold them into the dough.
Line a muffin tin with 12 muffin liners. Lightly grease each liner with a bit of spray oil or butter to prevent sticking (optional, I find these muffins stick less than other keto muffin recipes).
Using a muffin scoop, scoop batter evenly into the 12 cups.
Bake the blueberry muffins for 20-22min or just until the tops are lightly golden brown and they've risen nicely. You can check with a toothpick to make sure it comes out clean.
Let them cool in the tray for at least 10-15min before attempting to remove them. Serve warm with a side of butter and enjoy your Low Carb Lemon Blueberry Muffins!