16 tablespoons (2 sticks) unsalted butter, cut into chunks
3/4 cup granulated sugar
½ teaspoon raspberry extract or 1 teaspoon vanilla extract
Pinch of salt
1/2 cup plus 1 tablespoon all-purpose flour
1/2 cup powdered sugar
2 tablespoons unsweetened Dutch-process cocoa powder
Generously butter six or seven 3/4-cup soufflé dishes, ramekins, or shallow custard cups. In a microwave-safe medium bowl, combine the chocolate and butter. Microwave on high power for 1 minute, then stop and stir. Continue microwaving on medium power, stopping and stirring at 30-second intervals, until the chocolate and butter are barely melted, stirring occasionally; let the residual heat finish the job. (Alternatively, in a heavy medium saucepan, warm the chocolate and butter over lowest heat, stirring frequently, until partially melted; be very careful not to burn. Immediately remove from the heat.) Stir in 3 tablespoons jam until it melts and the chocolate mixture cools to warm.
In a large bowl, whisk the eggs and yolk until blended. Add the granulated sugar, extract, and salt, whisking until evenly incorporated. Whisk in the chocolate mixture. Sift the flour, powdered sugar, and cocoa powder over the batter and whisk until smoothly incorporated. If the batter seems very stiff and dry, stir in up to 2 tablespoons warm water. Divide the batter among the prepared dishes; they should be fairly full. The unbaked cakes will keep, covered, in the refrigerator for up to 48 hours.
Position a rack in the middle of the oven and preheat to 400 degrees F. Place the dishes on a rimmed baking sheet. Bake for 15 to 20 minutes (a little longer if the batter has been refrigerated), or until the tops are browner at the edges and rise above the dish rims. The center tops should be soft to the touch and look underdone, and the consistency pudding-like when a toothpick is inserted in the center. Run a paring knife around the dishes and under the bottoms of the cakes until completely loosened. Let cool on a wire rack for 6 to 7 minutes to cool slightly and firm up.To plate, center a dessert plate directly over a cake top. Using oven mitts and holding the two tightly against each other, invert the cake onto the plate. Repeat with the remaining cakes. Garnish the plates with drizzled melted raspberry jam, as shown, if desired. (I pipe it using a pastry bag or through a sturdy plastic baggie with a tiny hole snipped in one corner.) Serve immediately, garnished with lightly sweetened whipped cream (or with sifted powdered sugar over top) if desired.
Alternative do-ahead unmolding option: The warm chocolate cakes can be unmolded and placed all together on an ovenproof platter, covered, and set aside for a few hours. Reheat in a 325 degree F oven just until warmed through but not hot before serving. Transfer to individual dessert plates using a wide spatula.