Roast the unpeeled banana at 400°F (205°C) for 12 to 15 minutes, until the peel is mostly dark and the fruit feels very soft.
Add cane sugar and water to a small saucepan. Warm over medium heat, stirring until the sugar dissolves.
Split the roasted banana peel and scoop the soft fruit into the saucepan. Stir in the maple syrup.
Simmer gently for 7 to 8 minutes, stirring occasionally and pressing the banana once or twice with a spoon.
Strain through a fine-mesh sieve into a heat-safe container without forcing the pulp through. Stir in vanilla and salt, then cool completely before refrigerating.