Preheat oven to 400 degrees F. Line a large baking sheet with parchment paper.
Place one sheet of puff pastry on a lightly floured work surface, sprinkle with a little additional flour, and gently roll out into a 14-inch square.
Place the squares of chocolate evenly spaced over the pastry. Top each square of chocolate with two slices of banana. Spoon a ½ teaspoon of dulce de leche over each set of bananas.
Roll out the second sheet of puff pastry as you did the first, and lay it gently on top of the prepared pastry. Using a pizza cutter or ravioli cutter, slice between the chocolate/banana/dulce de leche pockets. Gently separate them and, using a fork, press along the edges to seal together.
Place the tartlets on the parchment-lined baking sheet, brush each with melted butter and sprinkle with sugar. Bake for 15 to 20 minutes, or until golden brown. Remove from the oven and allow to cool for at least 10 minutes before serving. Serve warm or at room temperature.
Notes
Make-Ahead Note: These can be assembled (through step #4), placed on a baking sheet and frozen. Once completely frozen, transfer to a freezer-safe ziploc bag and store for up to 2 months. Bake according to the direction in step #5, adding a couple more minutes to the baking time.Note: You can substitute caramel sauce if you are unable to find dulce de leche.Nutritional values are based on one tartlet