For the chocolate cakes:
1/4 cup sugar, plus 8 teaspoons for coating the ramekins
4 1/2 ounces bittersweet chocolate, divided
2 large eggs, whites and yolks separated and brought to room temperature
1/3 cup plain nonfat Greek yogurt
For the sauce:
1 1/2 cups fresh or frozen raspberries (if frozen, thaw, drain and retain the liquid)
1 1/2 tablespoons sugar
Coat eight 1/3- or 1/4-cup ramekins with cooking spray. Sprinkle about 1 teaspoon of sugar into each, swirling it around to coat the bottom and sides, then dumping out any excess.
Finely chop 2 1/2 ounces of the chocolate. Cut the remaining 2 ounces into 16 pieces, roughly the same size, then set those aside.
Bring a small saucepan of water to a bare simmer. Set a medium stainless steel bowl over it and add the 2 1/2 ounces of finely chopped chocolate to that. Heat, stirring occasionally, until the chocolate is melted.
While the chocolate is melting, in another medium bowl use an electric mixer to beat the egg yolks with 1 tablespoon of the sugar until they are thick and lemon colored, about 4 minutes. Set the bowl aside and clean the beaters well.
In a third medium bowl, use the electric mixer to beat the egg whites until they form soft peaks. Add the remaining 3 tablespoons of granulated sugar, a little at a time, and continue beating until the whites hold stiff peaks. Set aside.
Remove the melted chocolate from the heat. Add the yogurt and stir well. Add the egg yolk mixture and stir well. Add one third of the egg whites to the chocolate mixture, stirring well, then gently fold in the remaining egg whites until they are just combined with the chocolate mixture. Divide the batter among the prepared ramekins. Cover and chill for 1 hour.
While the cakes are chilling, heat the oven to 325 F and prepare the sauce.
In a blender, puree the raspberries with the sugar. Pour the mixture through a mesh strainer, using a silicone spatula to press the pulp. Discard the pulp and seeds. Thin the sauce with water or with the reserved raspberry liquid (if using frozen berries) until the sauce has a nice pouring consistency.
Remove the ramekins from the fridge, tuck 2 pieces of the cut chocolate into the center of each and bake in the middle of the oven for 15 to 18 minutes, or until just springy when touched. Let cool for 5 minutes, then unmold or serve in the ramekins. Serve drizzled with the raspberry sauce.
Nutrition information per serving: 140 calories; 70 calories from fat (50 percent of total calories); 8 g fat (3.5 g saturated; 0 g trans fats); 45 mg cholesterol; 20 g carbohydrate; 3 g fiber; 16 g sugar; 4 g protein; 20 mg sodium.