The full name for this delicious recipe is 'A high school bonfire chocolate melting heart cake - with a soft marshmallow first memory hidden inside'. It is from Chocolate: A Love Story, Max Brenner’s private collection of dessert recipes.
Make the ganache filling. In a small saucepan, cook the cream and the whole marshmallows until the marshmallows melt and the mixture comes to a simmer. Pour over the white chocolate in a heatproof bowl. Let sit until the chocolate begins to soften, about a minute, then stir until smooth.
Divide the ganache among fifteen 1 ½ inch round by 1-inch deep silicon moulds, sprinkling with the diced marshmallow as you go. Freeze for a minimum of 4 hours.
Prepare the soufflés. Preheat the oven to 400 degrees F. Melt the dark chocolate in a heatproof bowl set over simmering water (a bain-marie). Add the butter and sugar and stir until the mixture is smooth and warm. Remove from the heat and let cool. Whisk in the eggs one by one. Set aside.
In a separate bowl, sift together the flour, cocoa powder and baking powder. Whisk the dry ingredients into the chocolate mixture until smooth. Divide among 15 2 ½ inch paper baking cups, filling each ¾ the way full.
Put one frozen marshmallow ganache piece in the middle of each baking cup. Bake until the soufflés rise and the insides are still molten, about 9 minutes. Serve immediately.