Preheat the oven to 350 degrees and line a sheet pan with parchment paper.
In a large bowl, whisk the almond flour, coconut flour, sweetener, chia seeds and baking powder.
Stir in the milk, MCT oil, 1 egg plus 1 egg yolk (saving the white for step 5), lemon zest, and almond extract. Once combined, fold in the blueberries and sliced almonds.
Using a ¼ cup measure, scoop the batter onto the prepared pan. Using damp hands, form into a cookie shape, about 1 inch thick.
In a small bowl, whisk the remaining egg white and brush it on top of the cookies. Bake for 20-25 minutes until golden. Cool for 5 minutes on the pan, then transfer to a wire rack to cool completely.
Notes:
Store leftover cookies in a lidded container in the fridge for up to 5 days or on the counter for up to 3 days. Wrap individually and freeze for up to 3 months.