Mix the cornstarch with some of the milk until smooth. Whisk the egg yolks in a bowl, then add to the cornstarch mixture. Gradually stir in the remaining milk until well combined.
In a saucepan, combine the sugar and 50 ml water. Heat over high heat until boiling, then reduce to medium heat. Continue heating for about 7-10 minutes, stirring occasionally, until the sugar turns deep golden brown and caramelizes. Immediately remove from heat and very carefully add the 50 ml hot water (watch for steam). Immediately return the pan to medium heat and stir until the caramel becomes smooth and liquid.
Slowly pour the milk mixture into the caramel while stirring constantly. Increase heat to medium-high and bring to a boil, stirring frequently. Continue cooking for about 3-5 minutes, stirring often, until the mixture thickens significantly. Remove from heat.
Let the cream mixture cool to room temperature, about 15-20 minutes, stirring occasionally to prevent a skin from forming.
In a separate bowl, whip the 100 ml cream until stiff peaks form.
When the cream mixture is cool but still slightly warm (not completely cooled), carefully fold in the whipped cream until just combined.
Divide into serving dishes and refrigerate for at least 2 hours before serving.