Rub the cold butter into the flour, 25 g caster sugar and salt with your fingertips until the mixture looks like coarse breadcrumbs.

Mix in the egg yolk and 2 tbsp cold water, bringing the dough together with your hands. Add the extra tablespoon of water only if it feels dry. Wrap and chill for 30 minutes.

Roll the dough on a floured surface to about 3 mm thick and line a 23 cm / 9-inch tart tin. Trim the edges, prick the base with a fork, and chill for 15 minutes.

Heat the oven to 190 C / 375 F. Line the pastry with parchment and baking beans, and blind bake for 15 minutes. Remove the beans and paper, then bake for another 8 to 10 minutes until the base looks dry and pale gold, not shiny. Cool completely on a wire rack.

Toast the desiccated coconut in a dry 20 cm / 8-inch skillet over medium heat, stirring often, for 2 to 3 minutes until light golden. Tip onto a plate to cool.

Spread the raspberry jam evenly over the cooled pastry base. Arrange the sliced bananas in a single layer over the jam.

In a 2-quart / 1.9 L saucepan, whisk the custard powder and 40 g sugar with a splash of the cold milk to a smooth paste. Add the rest of the milk and the vanilla, then heat over medium, whisking constantly, until the custard thickens enough to coat the back of a spoon, about 4 to 5 minutes.

Pour the warm custard over the bananas and smooth the top with a spatula.

Sprinkle the toasted coconut evenly over the warm custard so it sticks.

Chill the tart uncovered for 30 minutes, then cover loosely and refrigerate for at least 3 hours, or overnight, until the custard is set firm but still creamy.

Slice with a knife dipped in hot water and serve chilled.