Mix flour, salt and sugar in a large bowl and add 200ml of lukewarm water gradually, to form a dough. Knead until elastic and shiny. Cover in plastic wrap and leave to rest for 20 minutes.
Divide into 8 balls, roll each in vegetable oil and put on an oiled plate. Cover and chill overnight.
The next day. Spread a dab of unsalted butter on your work surface. Take one ball and lightly flatten it with the heel of the palm of your hand to make it bigger. Stretch it as thin as possible, until you can almost see through it. You can spread additional room temperature butter on the roti dough to help the stretching.
Scrape and push the upper end of the dough to the middle. Do the same to the lower end, forming a wrinkle thin log. Starting at one end of the log, roll it into a circle and tuck the other end inside. Leave aside for 10 minutes before cooking. Meanwhile you can continue with the rest of the balls.
Once ready to cook, take one rolled roti dough and flatten it into approximately 10-15 cm diameter. Heat some unsalted butter on non-stick pan over medium heat. Place the dough on the pan. Cook for several minutes until browned and crispy then flip.
For fluffy roti canai, remove the cooked pancake and place it on a work surface. Immediately grab it using both of your hands and squeeze it to the centre.
Keep the roti canai under a kitchen cloth to keep them warm. They're best eaten with dhal curry.