Custard Cake (Leche Flan Cake)

Method

1. Heat the oven to 175°C. Set out two ungreased, solid-bottomed 15 cm round pans at least 7.5 cm deep; do not use springform pans. Boil water for the bath.
2. Simmer the caramel sugar and water without stirring, swirling as needed, until amber. Divide immediately between the pans and tilt carefully to coat the bases.
3. Whisk the flan ingredients gently to avoid foam. Strain over the hardened caramel, divide evenly, and skim off surface bubbles.
4. Beat the cake yolks with their sugar until pale, then whisk in oil, milk, and vanilla. Sift in flour, baking powder, and salt; mix just until smooth.
5. Beat the whites and cream of tartar to soft peaks. Add meringue sugar gradually and beat to glossy stiff peaks that do not look dry.
6. Fold one-third of the meringue into the yolk batter, then fold in the rest. Divide gently over the flan; the airy batter should float.
7. Set the pans in a roasting tray and add hot water halfway up their sides. Bake 35–45 minutes, until the cake springs back, a skewer in the cake is clean, and the flan has only a gentle central jiggle and reaches 71°C.
8. Remove from the bath and cool on a rack for no more than 1 hour, then cover and refrigerate in the pans for at least 4 hours or overnight. Start refrigeration within 2 hours of leaving the oven, or within 1 hour if the room is above 32°C.
9. Loosen the edges, warm each pan base for 10 seconds, and invert onto a rimmed plate. Slice cold and keep leftovers refrigerated.