For the cake layer:

1. Preheat your oven to 375 degrees (F)
2. Cream the butter and sweetener together in a medium bowl until smooth.
3. Add the eggs, beating well after each.
4. Add the vanilla extract and mix well.
5. Combine the almond flour, coconut flour, salt, baking powder, and xanthan gum in a separate medium bowl.
6. Add to the wet ingredients and mix well.
7. Pour in the almond milk and blend until smooth.
8. Grease a 9×9 (or equivalent) pan with butter.
9. Spread the cake batter evenly over the bottom of the pan.
10. Sprinkle the blueberries evenly over the top of the batter.

For the cream cheese mixture:

1. Heat the cream cheese for 30 seconds in the microwave until soft.
2. Beat with a fork until smooth.
3. Add the egg and sweetener and beat with a fork until smooth.
4. Pour over the top of the blueberries.

For the streusel topping:

1. Melt the butter in a microwave safe bowl or on the stove.
2. Stir in the almond flour, sweetener, and lemon zest until fully combined.
3. Crumble over the top of the cake.
4. Bake the cake at 375 degrees (F) for 35 minutes or until a knife inserted in the center comes out clean and the top is golden brown.