Preheat the oven to 350°F. Lightly grease 8 donut molds with canola oil.
In a small bowl, make “buttermilk” by combining the rice milk and cider vinegar. In another small bowl, mix together the water and flaxseed meal and allow to thicken for 3 to 5 minutes.
In a large mixing bowl, whisk together ½ cup of the granulated sugar, the baking powder, baking soda, salt, xanthan gum, and nutmeg. Stir in the flaxseed mixture and the “buttermilk” mixture. Gradually add the baking mix and stir until the dry ingredients are thoroughly combined but the dough is still soft. Spoon the dough into a large pastry bag fitted with a wide tip and pipe the batter into the prepared molds.
Place the molds on a baking sheet and bake for about 18 minutes, or until the donuts are golden and firm. Remove the donuts from the oven and turn them out onto cooling racks to cool.
Pour the confectioners sugar into 1 paper bag, and combine the cinnamon and the remaining ½ cup of granulated sugar the other bag. Drop the donuts into one bag or another and, holding the top of the bag tightly closed, shake the bag to thoroughly coat each donut. Serve immediately.
Variation: Fried donuts
Heat a couple of inches of canola oil in a deep pot to 360°F.
Prepare the donuts as instructed, but instead of spooning the batter into a pastry bag, carefully drop it by large spoonfuls into the hot canola oil, without crowding, and fry for 1 to 2 minutes per side, or until golden. Remove the donuts from the oil with a slotted spoon and drain them on paper towels. Continue with the remaining dough. Then continue with coating the donuts as instructed above. Serve immediately.