Preheat the oven and prepare the baking dish - Preheat your oven to 350°F (180°C). Bring a kettle of water to a boil for the water bath. Get a baking dish that can hold all your ramekins and place a kitchen towel at the bottom (this helps to prevent the ramekins from sliding around). Place the ramekins inside the baking dish and set aside.

Make the caramel sauce - In a saucepan over medium heat, add the sugar and cook until it turns into a rich amber color, stirring occasionally (this can take about 10-15 minutes). Remove from heat and add butter and salt, whisking until the butter is melted and combined. Let the caramel cool for a few minutes. - Be careful not to burn the sugar, as this will affect the taste of the caramel. Also, when adding the butter and salt to the saucepan, the mixture will bubble and sizzle, so be careful not to burn yourself. If you prefer a thicker caramel sauce, you can let it cool longer before adding it to the ramekins.

Make the Pot de Crème mixture - In a mixing bowl, whisk together the egg yolks and vanilla extract until pale and creamy. In another mixing bowl, whisk together the heavy cream and mashed bananas until well combined. Add the banana mixture to the egg mixture and whisk until smooth. - When whisking the egg yolks, make sure you don't overwhisk them, as this can result in a grainy texture. Also, make sure to mash your bananas well or they may result in lumps in the final product. If you want a stronger banana flavor, you can add an additional banana to the mixture.

Add the caramel sauce to the ramekins - Divide the caramel sauce among the ramekins, pouring it into the bottom of each one. - It's important to make sure you have an even layer of caramel sauce in each ramekin.

Add the Pot de Crème mixture to the ramekins - Pour the Pot de Crème mixture into each ramekin over the caramel sauce, filling them about 3/4 full. - Make sure to leave some room at the top of each ramekin, as the Pot de Crème will rise slightly when baked. Also, try to pour the Pot de Crème mixture in gently to avoid disturbing the caramel layer at the bottom.

Bake the Pot de Crème in a water bath - Place the baking dish with the ramekins in the preheated oven. Carefully pour the hot water into the baking dish, around the ramekins, until it reaches about halfway up the sides. Bake for 35-40 minutes, or until the Pot de Crème is set around the edges but still slightly jiggly in the center. - Be careful not to let any water spill into the ramekins or the Pot de Crème will become watery. Also, each oven is different, so adjust baking time accordingly. You can test if they are ready by gently shaking one of the ramekins - if the edges are firm and the center is slightly jiggly, then it's ready.

Chill and serve - Take the Pot de Crème out of the water bath and let them cool to room temperature. Then, chill them in the refrigerator for at least 2 hours (or overnight) before serving. Just before serving, sprinkle a pinch of sea salt on top of each Pot de Crème and use a kitchen torch to brûlée it (if desired). - If you don't have a kitchen torch, you can sprinkle the sea salt on top and skip the brûlée step. They will still taste amazing! Also, make sure to chill them for at least 2 hours to ensure they have a creamy and silky texture.