Preheat the oven to 385˚Linea baking sheet with parchment paper.
In a saucepan over low heat, melt the mozzarella and cream cheese together.
Stir until smooth and creamy.
Using an electric mixer, beat egg whites and cream of tartar until stiff peaks form.
Slowly fold in coconut flour, psyllium husk, and salt.
Knead with your hands until you achieve a dough-like consistency.
Add sparkling water and continue kneading.
Place the dough between two sheets of parchment paper, and roll the dough to ⅓-inch thickness.
Brush half of the melted butter onto the dough.
With a pizza cutter, start by dividing the dough into 4 equal squares, then into triangles that are about 4 inches wide at the bottom.
Roll the triangles up starting at the wide part and finishing with the point.
Place each croissant on the baking sheet at least 2 inches apart.
Brush the tops of the croissants with remaining butter, and bake them for 12 minutes or until golden brown.
Allow cooling slightly before serving.