Preheat krumkake iron. If using a stove-top iron, place over medium heat. Once hot rub both sides lightly with butter.
In a medium bowl, beat eggs until light. Slowly add sugar and beat until pale. Slowly add butter and vanilla. Stir in 1 ½ cups flour.
Test the batter on the hot iron. Place a scant tablespoon of batter towards the back of the iron and press down. The batter should spread across the entire iron without leaking out the sides. If the batter is too thin, mix in another ¼ cup of flour.
Each cookie will cook about 2 minutes per side (no need to flip if you have an electric iron). They should be a light golden brown. Once finished, remove with a thin knife and roll immediately on a wooden spoon handle, rolling pin, or cone. Allow them to cool before removing from the mold. Repeat with remaining batter.
To fill cooled cookies, pipe or spoon vanilla bean ice cream or desired filling carefully into the cookie. Eat filled cookies immediately or store plain cookies in an airtight container for up to several weeks.