To make truffles, place chocolate in a bowl. Heat cream over medium heat until steaming. Pour over chocolate and whisk together until smooth. Whisk in vanilla and refrigerate until mixture is firm enough to be molded. Create 8 equal-sized balls with the truffle mixture and place them on a baking sheet lined with waxed paper. Cover and place in freezer for 4 hours. (They can also be made ahead and kept frozen for up to a week.)
To make the cakes: lightly grease 8 ramekins (individual glass or ceramic baking cups), line bottoms with parchment paper and sprinkle with some of the sugar. In a bowl over a pot of hot (but not boiling) water, melt chocolate and butter. Let cool to room temperature. In a separate bowl, beat together eggs and yolks with sugar until thick (about 5 min.). Fold in warm chocolate and vanilla. Stir in flour. Fill each ramekin halfway. Put a frozen truffle in each, then top with rest of cake batter. Place ramekins on cookie sheet and bake in 350°F oven for 20 min. (until centre of cakes are slightly sunken, soft and shiny). Let cool for 2 min., then slide a knife around the edges of cakes and carefully tip cakes out of the ramekins and onto serving plates. Peel off paper and serve with dollop of whipped cream. (These cakes can be prepared and frozen unbaked for 24 hours, then baked right before serving.)