Preheat oven to 400 degrees F / 200 degrees C
Place the butter in a heat proof bowl and microwave until melted.
In a bowl, combine sugar, egg whites, vanilla and mix with whisk together.
Stir in the flour with melted butter and whisk until smooth
On a lined sheet tray, drop a teaspoon of batter at a time. Using the back of a spoon, spread the batter out thinly. The batter should be so thin you can see the parchment or lining.
Sprinkle chopped nuts or a pinch of flakey salt on top of each tuile.
Bake for 6-10 minutes or until edges are browned, making sure to turn the sheet tray halfway through.
The tuiles will be very malleable after it comes out of the oven and will harden fairly quickly. To shape the tuiles, use an offset spatula to lift and transfer the tuiles from the baking tray immediately after coming out of the oven onto a rolling pin. If you prefer to keep them flat and straight, wait for them to cool completely and they will come right off the sheet tray.
Store in an air tight container for up to 4 days.