In a large bowl whisk together the flour, confectioners’ sugar, baking powder and salt until combined.
In another medium bowl whisk together the milk, melted butter, vanilla and the egg yolk until thoroughly combined. Stir the milk mixture into the flour mixture until just combined.
In the bowl of a stand mixer fitted with a whisk attachment, beat the egg whites and cream of tartar on medium-high speed until the whites form stiff peaks, about 2 minutes. Fold the egg whites into the batter until just combined, being careful not to over mix.
Spray a 3-inch by 2½-inch high ring mold with vegetable cooking spray. Heat a large nonstick skillet over medium-low heat and spray the pan evenly with cooking spray. Place the ring mold in the pan and fill with ½ cup of the batter, it should fill the ring about halfway up.
Cover the skillet and cook until the batter rises and the bottom is golden brown, about 5 minutes.
Use a spatula under the mold and tongs around the mold to stabilize and carefully flip the pancake in the mold. Cover and continue to cook until the bottom is golden brown, another 5 minutes. Transfer to a plate and carefully remove the mold. Continue with the remaining pancake batter.