In a small saucepan, combine the pulverized xylitol and water. Heat over low-medium heat, stirring until the xylitol is fully dissolved.

Add the blueberries and lemon juice to the syrup mixture. Simmer for about 10 minutes, or until the blueberries start to break down and the mixture thickens. Remove from heat and set aside to cool.

In a mixing bowl, combine the almond flour, brown rice flour, pulverized xylitol, cold butter, and cinnamon.

Use your fingers or a pastry cutter to blend the ingredients until the mixture resembles coarse crumbs. Place the streusel in the refrigerator to keep it cold while you prepare the cake batter.

Preheat your oven to 180°C (350°F). Grease a round cake pan (about 9 inches in diameter) with coconut oil and lightly dust it with almond flour to prevent sticking.

In a large mixing bowl, combine the almond flour, amaranth flakes, white coconut flour, and powdered xylitol.

In another bowl, whisk together the eggs, coconut oil, coconut milk, and vanilla extract. (You can also beat the ingredients in a blender).

Pour the wet ingredients into the dry ingredients and mix until well combined, creating a smooth cake batter. (You can also add the dry ingredients to the blender and beat it until smooth). Add baking powder and mix it again.

Pour the cake batter into the greased cake pan, spreading it evenly.

Evenly distribute the prepared blueberry syrup over the cake batter.

Sprinkle the chilled streusel on top, covering the entire surface.

Place the cake in the preheated oven and bake for approximately 30-35 minutes or until the cake is golden brown and a toothpick inserted into the center comes out clean.

Remove the cake from the oven and let it cool in the pan for about 15 minutes. Then, transfer it to a wire rack to cool completely.

Once the cake has cooled, slice and serve. Enjoy your delicious Gluten-Free Blueberry Crumble Cake!