Gâteau Basque

Method

1. Make the pastry cream first. Bring the 90 ml of whole milk to a bare simmer in a small saucepan with the 0.25 tsp of vanilla extract. In a bowl, whisk the 1 egg yolk with the 15 g of caster sugar until pale, then whisk in the 7 g of plain flour to a smooth paste.
2. Pour the hot milk over the yolk mixture in a thin stream, whisking hard, then return everything to the pan over medium-low heat. Whisk constantly for about 2 minutes: it will thicken suddenly, then loosen slightly as the flour cooks out. Off the heat, whisk in the 1 tsp of dark rum. Scrape into a shallow dish, press cling film onto the surface and chill until cold, about 45 minutes.
3. For the pastry, beat the 35 g of softened unsalted butter with the 35 g of caster sugar until light and creamy. Beat in the 1 egg yolk and the 0.5 tsp of grated lemon zest. Sift over the 65 g of plain flour with the 0.25 tsp of baking powder and the 1 pinch of fine salt, and work them in with a spatula just until a soft, sticky dough forms. Shape into a disc, wrap and chill for 1 hour.