Mix flour, sugar, baking powder, and salt in a large bowl.
Mix ground flax seed with water in a medium-sized bowl, and let thicken up for about 5 minutes.
Add the milk, oil, and vanilla to the flax/water mixture and stir it well.
Add wet ingredients to dry ingredients. Don't overmix. Let the mixture set while preparing the pan.
Heat a nonstick pan on medium-high heat until hot.
When heated, add butter or oil and let it heat through. Then add about 1/3 cup of batter to the pan. Do not move pancakes until small bubbles start to appear on the edges. Gently lift an edge to check for golden color underneath. Then carefully lift the edges gently until your pancake flipper can easily go completely under the pancake. Then flip and finish cooking the other side, checking for doneness after about 1 minute. If pancakes are cooking too quickly, turn the heat down a notch. If the pan isn't completely nonstick, grease it well. Add in any mix-ins of your choosing. If you use different add-ins like chocolate chips, bananas, and berries, place them on the tops of the pancakes as they cook. But if you want the same add-ins in all the pancakes, mix them into the batter before pouring them onto the griddle.
To keep them warm as you finish cooking the rest of the batter, place a wire cooling rack inside the oven set to warm (or 170 degrees Fahrenheit.).Add the finished pancakes to the rack until ready to eat.