In a small saucepan, combine sweetened condensed milk, heavy cream and milk. Place over medium heat and let come to a boil. Reduce heat to medium-low and let simmer for 3 minutes or until thickened slightly (maintain the heat so that, the milk simmers yet doesn't boil over).
Take pan off heat, stir in vanilla extract and salt. Let it cool, until warm or room temperature (this sauce can be made ahead and stored at room temperature for a few hours or stored in refrigerator for 1-2 days).
Make waffles
Preheat your waffle iron according to manufacters instructions.
Whisk together all purpose flour, baking powder and baking soda in a medium bowl.
In another medium bowl, whisk egg, melted butter and milk until smooth. Add this wet mixture into the flour mixture and whisk to combine.
Grease the waffle iron with non-stick cooking spray. Ladle ⅓ cup of batter onto the hot iron and cook waffles according to manufacture's instructions , until golden in color.
Remove waffles and place on a wire rack (to maintain the crispness). Repeat to make remaining waffles.
Cinnamon sugar coating
Stir together sugar and ground cinnamon and place on a medium plate. Just before serving, brush one side of each waffle with melted butter and place buttered side down on the cinnamon sugar. Press slightly for the sugar to adhere well. Serve waffles with tres leches sauce on the side or drizzled on top.