Carefully separate the egg whites and egg yolks into two dry and clean bowls. (Be careful not to break the egg yolks during the separation process, as any water, oil, or yolk residue could prevent the egg whites from achieving the desired consistency when beaten. But a small amount of egg white in the yolk bowl is fine.)
Add pumpkin puree, milk (or water), and vegetable oil to the egg yolks. Mix with a whisk.
Sift the cake flour and baking powder (optional) into the bowl. Use a small spatula to mix gently until there's so dry flour. Set aside. (The consistency of this mixture should be similar to Greek yogurt. If it appears too dry, you can mix in an extra ½ tsp of milk to achieve a smoother texture.) Set aside.
Lightly grease a large nonstick pan with vegetable oil. Preheat it over medium-low to low heat. Add granulated sugar and lemon juice (optional) to the egg whites. Using an electric mixer, whip the egg whites on medium-high speed until stiff peaks form. (*Important Reminder: In case you've previously used the electric mixer to whip the cinnamon honey butter, it's essential to ensure the beaters are carefully washed and dried before using them to whip the egg whites. Any remaining butter on the beaters could hinder the egg whites from achieving their desired level of stiffness. ) Fold ⅓ of the whipped egg whites into the egg yolk mixture. Be careful not to deflate the egg whites; fold until just incorporated.
Pour the egg yolk & white mixture into the egg white bowl. Gently fold until the color of the batter turns evenly light yellow. Quickly transfer the batter into a piping bag.
Pipe the batter into 3 mounds into the preheated nonstick pan. (You can also use a spoon to place 3 scoops of batter into the pan. Then stack one scoop of batter onto each batter that's already in the pan. If you have more batter left, you can keep piling up the batter on the top of each pancake. Try to pile the batter as tall as possible, so that the pancakes will be fluffier.)
Add 1½ teaspoons of cold water in each of the three empty corners in the pan, distributing ½ teaspoon of water into each corner. Quickly cover with a lid. (The water can create a steaming environment, ensuring thorough cooking of the central part of the pancakes.) Keep the lid on for 5 minutes.
Open the lid, carefully flip each pancake using a spatula. Add 1½ teaspoons of cold water in empty spaces inside the pan. Cover with a lid. Keep the lid on for 3 more minutes.
Serve the pumpkin pancakes immediately while they are still fluffy and hot. Top them with your homemade cinnamon honey butter, maple syrup, or any other toppings of your choice.