In a large saucepan, pour in whole milk and heat over medium heat until it begins to simmer, then reduce heat to low and stir in half of the sugar until fully dissolved.

In a medium bowl, combine the remaining sugar and cornstarch. Whisk these together until smooth, then add in the egg yolks and mix well.

Gradually pour the egg yolk mixture into the simmering milk, stirring continuously with a whisk. Keep the heat low and monitor closely, as the custard will thicken after about 3-5 minutes.

Use a heat-safe thermometer to check the custard’s temperature while it thickens, aiming for about 185°F.

Once thickened, remove from heat and stir in softened unsalted butter, pure vanilla extract, and the mashed banana.

Strain the custard through a fine-mesh sieve into a bowl to catch any lumps. Cover with plastic wrap directly on the surface and refrigerate for at least 30 minutes.

Once chilled, stir the custard gently before serving. Optionally fold in sliced bananas just before serving.