1. Butter and dust with cocoa powder 5 ramekins (small oven-safe dishes, with or without handles). Melt the butter and chocolate in a double boiler (bain-marie). That is, put water in a small saucepan to reach 1/3 of its volume and bring it to a boil over heat. Place a glass bowl over the opening of the saucepan and put the butter and chocolate inside. Stir until the chocolate and butter melt. Add the eggs, yolks, salt, sugar, and vanilla to the mixer bowl. Beat for 5 minutes.
2. Turn off the mixer and pour a little of the egg mixture into the chocolate and incorporate with a spatula using circular motions. Add a little more, and finally the rest. Then, sift half of the flour into the bowl and incorporate with a spatula. Then sprinkle with the remaining flour. Divide the mixture into the ramekins (100 gr. of the mixture in each) and bake in a preheated oven at 200°C (392°F) for 10 minutes.
3. Let them cool for 2-3 minutes and score around the edges with a sharp knife. Turn them upside down and serve with whipped cream or ice cream and sliced strawberries or raspberries.
