In the top of a double boiler, melt the chocolate, then add the butter and sugar until just melted. Add eggs and whisk until well combined; add flour and mix only until combined. Do not overmix or the cake will be rubbery. Lightly grease four 4-ounce disposable aluminum cups, muffin molds, or ramekins with vegetable baking spray. Distribute batter among the four molds. Place molds on a sheet pan and bake for 10 to 12 minutes. Do not overbake.
For the Chocolate Sauce: Pour the milk into a 2-quart heavy-bottomed saucepan, place over medium-high heat, and bring to a boil. When it boils, remove the milk from the heat and make a ganache by adding the chopped chocolate. Whisk well, stirring into the edge of the saucepan to combine. The ganache should be homogenous and smooth. Set the ganache aside.
In a 1-quart heavy-bottomed saucepan, combine the heavy cream, butter, and sugar. Place the saucepan over medium-high heat and bring to a boil, stirring occasionally. The butter should be completely melted and the sugar completely dissolved. Once the mixture has come to a boil, pour it into the warm ganache. Place the sauce over medium-high heat and bring to a boil, stirring constantly with a whisk. As the chocolate sauce cooks, it will begin to thicken slightly. When it reaches a boil, remove it from the heat, and pour it into a clean, dry bowl. Cover by placing plastic wrap directly on top of the sauce to prevent a skin from forming. Let the chocolate sauce cool to room temperature before storing in the refrigerator. When cold, the sauce will become thick enough to be scooped with a spoon.
Invert molds onto individual serving plates. If you would like to decorate the plate, do so with fresh raspberries or fruit or chocolate sauce, and serve immediately.
The sauce can be reheated whenever needed. If using a microwave, simply place the chocolate sauce in a microwaveable bowl and heat it at medium-high power in 30-second intervals until it becomes liquid. On the stovetop, place in a heavy-bottomed saucepan over medium heat and stir occasionally until it becomes liquid. If you store it in a squeeze bottle, you can easily drizzle it over a dessert or decorate a plate. It will keep in the refrigerator for up to three weeks. It can also be frozen for up to two months if stored in an airtight container. Thaw in the refrigerator and heat as described above until liquid.