Combine flour, cake mix, baking powder, sugar and salt in a bowl and mix. Add 1 cup of milk, egg and vanilla extract and stir until smooth. You want the batter to look like regular pancake batter; not too thin, not too thick. This will vary greatly on the brand of cake mix you use. Start with 1 cup of milk and add more if needed. I suggest a small taste test as well to see if the pancakes are flavored enough.