Place the large egg in a mixing bowl and whisk with an electric whisk for about 1 minute until frothy.
Add the ricotta, grated Parmesan and a pinch of salt to the bowl and whisk until smooth and combined.
Sprinkle the coconut flour evenly over the surface, then scatter the xanthan gum and psyllium husk powder on top; whisk briefly and finish combining with a spatula until a soft dough forms.
Chill the dough in the refrigerator for 1 hour (or freeze about 15 minutes) until firm enough to handle; alternatively refrigerate covered overnight.
Turn the chilled dough onto a lightly oiled surface, shape into a ball and cut into quarters. Oil your hands and roll each quarter into a thin log, then cut into 1–1.5 inch (2.5–3.8 cm) pieces.
If using a gnocchi board, gently press and roll each piece to create ridges; if using a fork, roll each piece into a ball and press with the fork to form ridges.
Place formed gnocchi on a parchment-lined baking tray and freeze for about 20 minutes, until firm but not rock hard.
Heat the butter in a large frying pan over medium heat, add the minced garlic and fry the gnocchi on one side about 1.5 minutes, then turn each piece, add the sage leaves and cook another 1.5 minutes until golden on both sides.
Season with cracked black pepper and additional salt if needed, then serve immediately.