Remove the cinnamon sticks and the cloves from the syrup and add the vanilla. Carefully (because it will bubble a lot) add the syrup in the pot with the semolina mixture. Return to the heat and cook stirring constantly until the mixture thickens and it starts to pull away from the sides of the pot. Lightly oil an 8-inch round pan. Spoon the halva into the pan and press it with the back of the spoon or a spatula until the surface is level. Let it cool for 30 minutes, invert it onto a serving plate, and transfer it in the fridge to cool completely.
Using an electric mixer (or even a whisk) whip the chocolate ganache until soft peaks form. Don't over-whip (keep in mind that it will become more firm once refrigerated again). Transfer into a piping pag and pipe it over the halva, or using a spatula spread it on an even, thick layer. Optionally, dust with cocoa powder. Eat!
If you pipe the whipped chocolate ganache you will probably have some leftover which you can serve by scoops next to each slice. Otherwise, you can make half the recipe of the mousse:
If you accidentally over-whip the ganache and becomes too stiff, you can heat it briefly in the microwaves until it becomes soft again (or even melt it completely and start over).