Source: "Chocolate" by Linda Collister
adapted by http://theresalwaysthyme.blogspot.com
Dark Chocolate Filling:
3 oz. bittersweet chocolate, chopped
1/3 cup heavy cream
White Chocolate Filling:
3 1/2 oz. white chocolate, chopped
1 1/2 sticks unsalted butter, at room temperature
3/4 cup sugar
3 extra large eggs, beaten
1 2/3 cups self-rising flour
a pinch of salt
1/2 teaspoon vanilla extract
about 1/4 cup milk
an ice cube tray, oiled
6 small dessert molds, 2 1/2 inches diameter, well buttered
The chocolate filling should be made at least 1 hour before making the sponge (though the filling can be kept in the freezer for up to 1 week). Put the chocolate into a heatproof bowl set over a saucepan of steaming but not boiling water and melt gently (do not let the base of the bowl touch the water) Remove the bowl from the heat and stir gently until just smooth. Stir in the cream, then pour into the prepared ice cube tray to make 6 "cubes." Freeze for at least 1 hour.
When ready to make the dessert, put the white chocolate into a heatproof bowl set over a saucepan of steaming but not boiling water and melt gently (do not let the base of the bowl touch the water). Remove the bowl from the heat and stir gently until just smooth, then let cool.
Put the butter into a large mixing bowl and, using a wooden spoon or electric mixer, beat the butter until creamy, then gradually beat in the sugar. When the mixture is very light and fluffy, beat in the eggs 1 tablespoon at a time, beating well after each addition. Using a large metal spoon, carefully fold in the flour and salt, followed by the melted chocolate, vanilla extract, and just enough milk to give the mixture a firm dropping consistency. Spoon the mixture into the prepared molds to fill by about half. Turn out the dark chocolate cubes, put one into the center of each mold, then top up with more sponge mixture so each one is three-quarters full.
Stand the molds in a roasting pan, then cover loosely with well-buttered foil. Bake in a preheated oven at 350°F for about 25 minutes or until just firm to the touch. Run a round-bladed knife inside each mold to loosen the edges, then carefully invert onto individual plates. Serve immediately.