Begin with the chocolate layer, as it needs time to cool properly.

In a small saucepan, combine the sugar, cocoa powder, and gelatin. Whisk them together first so everything is evenly distributed. Pour in the cold water and milk, then place the pan over medium heat. Stir continuously as it warms, making sure the mixture stays smooth and free of lumps. Bring it just to a boil, then remove it from the heat straight away. Set it aside and allow it to cool completely to room temperature, which will take about an hour and a half.

Now prepare the vanilla mousse base.

In a clean saucepan, add the milk, vanilla extract, and gelatin. Whisk well to dissolve everything evenly. Warm the mixture over medium heat while stirring constantly until it becomes steamy. Do not let it boil. Once it is hot and fully combined, take it off the heat and let it cool until it is only slightly warm to the touch. For faster cooling, pour it into a wider dish.

When the milk mixture has cooled, move on to the cream.

In a large bowl, whip the heavy cream with an electric mixer until it becomes light, airy, and holds soft peaks, about one and a half to two minutes on high speed. In a separate bowl, mix the sugar and sour cream until smooth and fully combined. Gently fold in the whipped cream.

With the mixer on low speed, slowly pour in the warm milk mixture. Scrape down the sides of the bowl to ensure everything blends evenly, then mix briefly until silky and uniform.

Work quickly now, as the mousse begins to set fast. Divide the mixture evenly into six serving glasses and place them in the refrigerator. Chill for at least 30 minutes, until lightly set.

Once firm, spoon about 3 to 4 tablespoons of the cooled chocolate sauce over each portion. Arrange five raspberries in a neat circle on top of the chocolate layer.

Return the cups to the refrigerator and allow them to set fully for about 4 to 5 hours before serving.