Make the pasta dough by whisking together the gluten free flour, xanthan gum, and salt in a large bowl. Create a well in the center and add the eggs and olive oil. Stir with a fork, gradually pulling the flour into the center, until a shaggy dough forms.
Knead the dough on a lightly floured surface for 2 to 3 minutes until smooth and pliable. Wrap it in plastic wrap and let it rest at room temperature for 30 minutes. While the dough rests, prepare the filling. Stir together the ricotta, parmesan, egg yolk, basil, nutmeg, salt, and pepper in a bowl until smooth and well combined. Refrigerate until ready to use.
Divide the dough in half. Roll out one piece on a generously floured surface until it is very thin, about 1/16 inch thick. Place tablespoon-sized mounds of filling about 2 inches apart across the sheet of dough.
Roll out the second piece of dough to the same thickness and carefully lay it over the filling mounds. Press down firmly around each mound of filling with your fingers to seal the dough and push out any air pockets. Cut into individual ravioli using a pastry wheel or round cutter.
Bring a large pot of generously salted water to a gentle boil. Carefully drop the ravioli in batches into the water and cook for 3 to 4 minutes, until they float to the surface and the edges are tender. Lift them out with a slotted spoon and set aside.
Melt the butter in a large skillet over medium heat. Add the garlic and sage leaves and cook for 1 to 2 minutes, until the butter begins to brown and the sage crisps slightly. Add the cooked ravioli to the skillet and gently toss them in the brown butter sage sauce.
Serve the ravioli topped with extra grated parmesan cheese and a few sage leaves.