Gently wash the banana leaves and pat them dry. Cut them into 6x12-inch (15x30 cm.) rectangles and briefly pass them over a flame or hot stovetop burner to make them more pliable.
In a mixing bowl, combine the glutinous rice flour, coconut milk, brown sugar, salt, and vanilla extract. Stir well until the ingredients are thoroughly blended.
Mix in the drained young coconut strings, ensuring an even distribution.
Take a piece of the prepared banana leaf and place a generous spoonful of the batter onto the center. Roll the banana leaf around the batter, creating a neat tube with open ends. Secure the ends by folding them inwards towards each other, pinching the sides of the open ends together, and then skewing each side with a toothpick to prevent it from unfurling as the tupig cooks.
Reheat a large skillet over medium heat. After 90 seconds when the pan is hot, place as many tupig into the pan as you can fit.
Cook the tupig for 15-17 minutes on each side. The outside should look dark brown before you flip them, and the Tupig becomes firm and cooked through.
Allow the tupig to cool and firm up slightly before unwrapping and serving.