In a medium saucepan over medium heat, combine milk, panela, and cinnamon. Stir gently for about 5 minutes until panela dissolves.

In a small bowl, whisk together cornstarch and cold milk until smooth to avoid lumps. Set aside.

Pour the cornstarch mixture into the warm milk while stirring with a whisk, stirring for 2-3 minutes until thickened.

Lower the heat and stir constantly for about 10-15 minutes until the custard coats the back of a spoon.

Remove from heat and stir in butter until melted and incorporated.

Pour the custard into a greased dish or bowls, let cool for 30 minutes, then chill in the refrigerator for at least 2 hours.

Before serving, garnish with grated coconut and cinnamon. Slice into squares or serve in bowls.