Prep the cups: Set out 6–8 small dessert cups or jars (6–8 ounces each). If using a cookie base, add a spoonful of crushed cookies to each cup and lightly press to form a loose layer.

Warm the dairy: In a medium saucepan, combine 2 cups milk and 1 cup heavy cream. Heat over medium until steaming, not boiling. Stir occasionally to prevent scorching.

Whisk the yolks: In a mixing bowl, whisk together egg yolks, granulated sugar, cornstarch, and salt until smooth and slightly pale. This creates a thick paste that will help thicken the custard.

Temper the eggs: Slowly ladle about 1/2 cup of the hot milk mixture into the yolk mixture while whisking constantly. Repeat with another 1/2 cup. This prevents curdling.

Thicken the custard: Pour the tempered yolk mixture back into the saucepan. Cook over medium heat, whisking steadily, until the custard thickens and bubbles gently, 3–5 minutes. It should coat the back of a spoon.

Finish and cool: Remove from heat. Whisk in vanilla extract and butter until smooth. Transfer to a shallow dish. Press plastic wrap directly on the surface to prevent a skin. Cool 20–30 minutes at room temperature, then chill until cool to the touch.

Whip the cream: In a cold bowl, whip 1 cup heavy cream with powdered sugar to soft peaks. For a lighter dessert, fold half of the whipped cream into the cooled custard. Reserve the rest for topping.

Prep the bananas: Slice bananas just before assembly. For slower browning, gently toss slices with a little lemon juice and pat dry.

Layer the cups: Spoon a layer of custard into each cup. Add banana slices in a single layer. Repeat with more custard and bananas, leaving space at the top for whipped cream. Aim for 2–3 layers.

Top and chill: Spoon or pipe whipped cream over each cup. If you like, add cookie crumbs or a thin banana slice on top. Chill at least 1–2 hours to set.

Serve: Serve cold. For clean layers and the best spoon feel, enjoy within 24 hours.