Peel and dice the potatoes. Place the potato dices into a small pot and cover with water. Add in a little salt, bring to a boil and simmer until the potato has softened.
Drain the potato dices into a colander and set the colander on top of the pot to allow the potato dices to steam dry.
Once the potato has cooled down slightly, transfer to a mixing bowl. Mash the potato dices and mix in the melted butter (best to go through a potato ricer if you have one). Let cool till warm then whisk in the egg whites until fully incorporated. Strain the mixture into a clean bowl then whisk in the salt, pepper and herbs.
Preheat the oven to 175 degrees Celsius. Line a baking sheet with baking parchment.
Spread a teaspoon of tuile mixture thinly on the baking parchment with the back of a spoon. You can use a template if you want perfect circles. Use more mixture if you'd like a bigger tuile.
Bake for 10 to 12 minutes until the tuile is golden brown in colour.
Soak the diced onion in cold water for 15 minutes. Drain well. This will help to get rid of the bite of the onion.
Combine the cooled prawns, chopped onion, chopped cherry tomatoes and cilantro leaves together. Add in a little olive oil and lime juice and toss well. Season with salt and pepper. Taste if it needs more oil or lime juice and adjust to your liking. Cover and set in the refrigerator for at least 30 minutes. for the flavours to mingle.