For cake: Cut up butter and chocolate and melt with unsweetened chips in a double boiler over low heat. Whisk together cornstarch and sugar in a stand mixer bowl. Stir melted chocolate into cornstarch mixture. Using the stand mixer on low speed, whisk in whole eggs, yolks and orange liqueur until smooth. Put in a clean container and refrigerate overnight.
Preheat oven to 350 degrees. Line flat sheet pans with parchment paper. Butter and sugar six 4-oz. baking ramekins and place on sheet pans. Fill ramekins with mixture all the way to the top. Bake for 20 to 25 minutes. They should not be set in the center and top should be slightly transparent. Cool to room temperature.
For chocolate sauce: Bring cream to a boil, then remove from heat. Add chocolate to hot cream. Stir until melted. Once the mixture has come together into a smooth sauce, add vanilla and orange liqueur. Cool sauce in refrigerator until solid. (You may want to prepare sauce a day ahead of time, perhaps when making the meltdown mix.)
Once the cakes have cooled to room temperature, use a tablespoon to place 1 scoop of chocolate sauce in the center of each cake where it has collapsed. Bake at 350 degrees for 5 more minutes or until the sauce has melted into the center. Serve meltdowns immediately with the leftover chocolate sauce, which can be melted in a saucepan over low heat or placed in the microwave for 45 seconds.
Additional accompaniments can include fresh raspberries, whipped cream, caramel sauce and crème anglaise.
Because of her interest in locally grown products, Hosmer uses raspberries from Watsonville in this recipe.