Make the crust. Mix crushed biscuits, melted butter, brown sugar, and a pinch of salt in a bowl until it looks like wet sand. Press firmly into the base and up the sides of a 9-inch (23 cm) pie dish. Use a glass to compact it well.

Chill the base. Refrigerate for at least 20–30 minutes so it firms up. A solid crust keeps the filling from loosening it later.

Cook the toffee. In a medium saucepan, melt butter and brown sugar over medium heat. Stir in the sweetened condensed milk and cook, stirring constantly, until the mixture thickens and turns a light caramel color, about 6–8 minutes. Do not let it boil hard, and keep it moving to avoid scorching.

Finish the caramel. Remove from heat and stir in vanilla and a pinch of sea salt. The salt deepens flavor and keeps it from being too sweet.

Fill the crust. Pour the warm toffee into the chilled crust and spread evenly. Let it cool to room temperature, then chill for 1–2 hours until set.

Slice the bananas. Cut into coins or slight diagonals. If you’re making the pie ahead, toss slices lightly with lemon juice to slow browning, then pat dry.

Whip the cream. Beat cold cream with icing sugar and vanilla to soft or medium peaks. You want it billowy, not stiff.

Assemble. Layer bananas over the chilled toffee. Spoon or pipe the whipped cream on top. Add chocolate shavings or a dusting of cocoa if you like.

Chill briefly. Refrigerate 30 minutes to settle, or serve right away if everything is cold and set.

Serve. Slice with a warm, thin knife for clean pieces. Wipe the blade between cuts.