In a large non stick saucepan, stir well the sweetened condensed milk with the melted butter. Cook over medium heat, stirring constantly with a wooden spoon, for about 10-15 minutes or until mixture has thickened and starts pulling away from the bottom of the pan.
Remove from the heat and stir in both the vanilla and 1/2 cup of heavy cream until obtaining a creamy, homogeneous mixture. Let cool for about 10 minutes and then place 2 Tablespoons into each shot glass.
In a medium bowl, stir in the remaining 1/4 cup of heavy cream with 1/2 can of dulce de leche until obtaining a homogeneous mixture. Place 1-2 tablespoons of the dulce de leche mixture into each shot glass. Top with 2 Tablespoons of the cooked condensed milk mixture.
Mix the sugar with the cinnamon in a small bowl. Sprinkle about 1-2 teaspoons of the sugar-cinnamon mixture on top of each trifle, and then pipe beaten whipped cream on top -- only if desired. Refrigerate and serve either as prepared or drizzled with any remaining dulce de leche/heavy cream mixture. YIELD: 7-9 shot glasses