Preheat the oven to 400F. Have ready four 1/2-cup ramekins, muffin molds, or disposable aluminum cups. If they are not nonstick, lightly coat them with nonstick baking spray. Arrange the ramekins on a rimmed baking sheet. In the top half of a double boiler, combine the chocolate, butter, and sugar. Place over (not touching) barely simmering water in the bottom pan and heat, stirring constantly with a wooden spoon, until melted, fully blended, and smooth. Add the eggs one at a time, whisking well after each addition. Remove from the heat and add the flour, stirring just to combine.
Divide the batter evenly among the ramekins, and place the baking sheet in the oven. Bake for 12 minutes, or until just set, slightly cracked on top, and gooey in the interior. Do not over-bake, or the cakes will be too firm. Remove from the oven and let stand for about 5 minutes.
Pool about 2 tablespoons of the warm sauce in the center of each dessert plate. Invert a ramekin over each pool of sauce, tapping it gently with your fingers to unmold the warm cake. Sprinkle each plate with an equal amount of the raspberries and serve immediately.