Dissolve the sugar in the water and milk and bring it to a bare simmer.
Boil for 5 minutes and remove from heat.
At the same time, brown the semolina in the oil on medium-high heat, stirring continuously.
This should take 4-5 minutes. Add the nutmeats for the last 2-3 minutes to toast them slightly.
When the semolina has taken a golden brown colour, add the syrup to it (taking care not to burn your hands, as this bubbles and steams up excessively- be prepared!), turn down the heat and keep stirring until you get a kind of thick porridge. Continue cooking until the mixture is very thick and pulls away from the sides of the pan as you stir.
Spoon into a buttered or oiled bundt pan and pack down with the back of a spoon. Let it cool. (I use a silicone bundt pan for this - eliminates the need to grease, and my halvah comes out in a pretty pattern).
Unmold onto a platter and sprinkle with more walnuts, toasted sesame (optional) and cinnamon.
You should not put this dessert in the refrigerator.
It can keep for a few days outside the refrigerator, assuming you can gather enough will power not to eat it all at once.
Some oil may start to drain off after a day or so, but this is to be expected, just dab it away with some kitchen paper.