Stir coconut milk and vinegar together in a bowl; set aside until the coconut milk tastes sour, about 5 minutes.
Mix flour, sugar, baking powder, baking soda, and salt together in a large mixing bowl.
Beat egg and melted butter into the coconut milk mixture; pour into the flour mixture and whisk together until no lumps remain in the batter.
Prepare a large skillet with cooking spray and place over medium heat.
Ladle batter into the skillet 1/4 cup at a time; cook until bubbles appear on the top of the pancake, about 5 minutes. Flip the pancake and continue cooking until the bottom is browned and the center is cooked through, 2 to 3 minutes more.