Begin by preparing the halva. In a large pan over medium heat, melt the butter.
Once the butter is melted, add the semolina and sugar to the pan. Stir continuously until the mixture turns a golden brown color.
In a separate container, heat the milk until it is hot but not boiling. Add the hot milk and cocoa powder to the semolina mixture, stirring constantly to prevent lumps from forming.
Reduce the heat to the lowest setting and continue to cook the mixture, stirring occasionally. Allow it to steam until it solidifies into a thick, paste-like consistency.
While the halva is cooking, prepare the whipped cream. In a mixing bowl, combine the heavy cream, milk powder, and lemon zest. Using an electric mixer, whip the mixture until it thickens and forms stiff peaks. Place the whipped cream in the refrigerator to keep it chilled.
Once the halva is ready, line a cooking ring with wax or parchment paper on the inside to prevent sticking.
Transfer the halva mixture into the prepared cooking ring, pressing it down to form an even layer.
Remove the whipped cream from the refrigerator and spread it over the top of the halva within the ring.
Carefully arrange fresh blueberries on top of the whipped cream to create an attractive presentation.
Gently remove the cooking ring and paper from around the halva.
Serve the semolina halva with cocoa immediately, or chill it in the refrigerator before serving to allow the flavors to meld together.