In a saucepan, combine the mashed bananas, sugar, lemon juice, and salt over medium heat. Stir until the sugar dissolves.

Add the cubed butter and stir until melted and combined.

In a mixing bowl, whisk the eggs. Gradually add a small amount of the warm banana mixture to the eggs, whisking constantly to temper them.

Slowly pour the egg mixture back into the saucepan while whisking continuously.

Cook over medium heat, stirring constantly, until the mixture thickens and coats the back of a spoon, about 10-15 minutes.

Remove from heat and strain the mixture through a fine-mesh strainer into a clean jar to remove any lumps.

Let the curd cool to room temperature, then refrigerate until set.