In a large mixing bowl, combine the flour, sugar, and salt. Add the cold butter cubes and use a pastry cutter or your hands to cut the butter into the dry ingredients until the mixture resembles coarse crumbs.
Gradually add the ice water, 1 tablespoon at a time, and mix until the dough comes together. Be careful not to overmix. Shape the dough into a disc, wrap it in plastic wrap, and refrigerate for at least 30 minutes.
Preheat your oven to 375°F (190°C). On a lightly floured surface, roll out the chilled dough to a thickness of about 1/8 inch. Use a round cookie cutter or a glass to cut out circles that will fit into your tartlet pans.
Gently press the dough circles into the tartlet pans, making sure to cover the bottom and sides evenly. Trim any excess dough. Place the tartlet pans on a baking sheet and set aside.
In a medium saucepan, mash the bananas with a fork until smooth. Add the lemon juice, sugar, cornstarch, and cinnamon (if using). Cook the mixture over medium heat, stirring constantly, until it thickens and comes to a boil. Remove from heat and let it cool slightly.
Spoon the banana filling into the prepared tartlet pans, filling them about three-quarters full. Smooth the tops with a spatula. Place the baking sheet with the tartlets in the preheated oven and bake for 15-18 minutes, or until the crust is golden brown.
Once baked, remove the tartlets from the oven and let them cool in the pans for a few minutes. Carefully transfer them to a wire rack to cool completely. If desired, garnish with a dollop of whipped cream and a fresh mint leaf before serving.