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. Place a glass bowl over the opening of the saucepan and put the butter and chocolate inside. Stir until the chocolate and butter have melted. In the mixer bowl, add the eggs, egg yolks, salt, sugar, and vanilla. Beat for 5 minutes.
2. Lower the speed 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 in the remaining flour.
3. Divide the mixture into the ramekins (100g of mixture in each) and bake in a preheated oven at 200°C (392°F) for 10 minutes. Let them cool for 2-3 minutes and score around the edges with a sharp knife. Turn them out onto plates and serve with whipped cream and sliced strawberries.
