1. Make sauce: Place raspberries in a large bowl and stir in lemon juice and sugar. Use a fork to mash until sugar is dissolved and sauce is chunky. Cover and chill well before serving.
2. Make cakes: Preheat oven to 425°F. Butter 8 3/4-cup ramekins or custard cups. Dust with sugar and tap out excess. Place on a large baking sheet.
3. Melt 12 Tbsp. butter with chocolate in top of a double boiler over barely simmering water, stirring often. Remove from heat and let cool slightly.
4. Using an electric mixer on medium-high speed, beat eggs and egg yolks with sugar and vanilla until light and fluffy, about 6 minutes. Fold in flour and chocolate mixture. Divide batter between ramekins and bake until firm yet slightly soft in center, 10 to 12 minutes. Do not overbake.
5. Run a knife around outside of cakes to loosen and carefully turn out onto small plates. Serve warm with raspberry sauce.
Be sure not to overbake these cakes; they should be firm on the outsides and slightly soft in the centers. .