For the Truffles: Combine the chocolate, cream, and butter in a small heatproof bowl, set over simmering water, and let melt. When almost melted, remove from the heat and stir the mixture until smooth. Stir in flavoring of your choice and refrigerate until thick enough to mound on a spoon, stirring occasionally, about 30 minutes.
Line a baking tray with waxed or parchment paper. Scrape the chocolate mixture into pastry bag fitted with a #3 plain tip. Pipe eight 1-inch mounds onto the prepared tray. Place 1 raspberry in center of each chocolate mound and pipe a little more of the chocolate mixture to enclose completely. Refrigerate until firm, about 15 minutes.
For the Cake: Position a rack in the center of oven and preheat oven to 350 degrees. Butter, or coat with vegetable spray, 8 oversize muffin cups (4 inches wide and 2 inches deep) or 1 1/4 cup custard cups. Line bottoms with rounds of waxed paper. (To cut out the rounds, place 1 of the cups on waxed paper and trace rounds the bottom with a pencil. Then cut the 8 circles.) Set aside.
In the top of a double boiler or a small heatproof bowl set over simmering water, melt together the chocolate and butter. Cool slightly.
Meanwhile, in the large bowl of an electric mixer. with a paddle or beaters, on high speed, beat eggs, egg yolks, and sugar until tripled in volume, about 5 minutes. Scrape in the chocolate mixture and, on low speed, beat just until combined. Remove the bowl and fold in the flour, using a rubber spatula. Spoon a little of the batter into each of the prepared cups top with 1 truffle, and cover with the remaining batter. Arrange cups on a baking tray and bake until edges of the cakes begin to pull away from the sides of the cups, 12 to 13 minutes. Let stand 10 minutes. Invert onto individual dessert plates and carefully peel off paper.
Serve warm Spoon softly whipped cream or ice cream next to each cake and, if desired, garnish with a few fresh raspberries. Serve immediately.