In a mixing bowl, beat the eggs. Add the buttermilk, butter, and vanilla extract to the eggs and whisk everything together. Use buttermilk and eggs that aren't cold to prevent the butter from clumping. Make sure that the butter isn’t hot as it might cook the eggs.
Combine the flour, baking powder, baking soda, sugar, and salt in a separate bowl.
Add the dry ingredients to the wet ingredients. Mix just until the dry ingredients are incorporated with the wet ingredients. Do not over-mix the batter as it will cause gluten to develop which will make the pancakes chewy instead of light and fluffy.
Fold the grated Granny Smith apple and apple whiskey into the batter using a spatula.
Let the batter rest for at least 5 minutes. It will allow the gluten that formed to relax a bit and get rid of some of the lumps in the batter.
Heat butter or oil in a frying pan over medium heat. You can pour a bit of the batter onto the frying pan to test that the heat is at the right temperature; if the temperature is right, the bottom of the batter won’t burn right away or take more than 2 minutes to brown.
To make your first pancake, pour some of the batter onto the frying pan. The pancake is ready to flip when lots of bubbles form at the top and start to pop.
Gently flip the pancake with the spatula when it's ready to turn. Set the pancake aside once it's done.
Continue to pour batter onto the frying pan to make pancakes until you’ve used up all of the batter. You might need to add more oil or butter to the frying pan between pancakes to prevent the batter from sticking to the pan.