In a bowl, whisk together the flour, sugar, and salt until well combined. Then, add the eggs and continue mixing until the batter is smooth and lump-free.
Stir in the melted unsalted butter gently, ensuring it is fully combined with the batter for a rich flavor.
Gradually pour in the whole milk, mixing until you achieve a smooth batter. If you're feeling adventurous, add the optional dark rum for an extra dimension of flavor.
Preheat a non-stick skillet over medium-low heat. Once warm, coat the surface with a touch of melted butter to prevent sticking.
Pour ¼ cup of batter into the center of the pan. Quickly swirl the pan to evenly distribute the batter. Cook for about 1-2 minutes, until the edges turn golden brown, then carefully flip the crepe.
Cook the second side briefly until lightly browned—just about 30 seconds. Stack the finished crepes on a plate, placing parchment paper between each one to keep them from sticking together.