To make the dough: In a large bowl, combine the semolina, sugar, and baking soda. Using your hands, mix well to infuse the ingredients. Add 150 ml of the cold sugar syrup and mix well with your fingertips, allowing the syrup to penetrate the semolina mixture. Add the powdered milk, if using.
Gradually add the water (350 ml) and mix with your hands until you achieve a thin, dropping consistency—not a liquid dough.
Grease a round baking tray (38 cm / 15 inches) evenly with both tahini/sugar syrup and ghee, making sure to coat the bottom and sides well. Transfer the dough to the greased tin and spread it into an even, level layer. Gently shake the tin to help distribute the batter evenly.The batter should be approximately 1½ cm / ½ inch deep. This will give you a moderately thick namoura. Keep in mind that the batter will rise slightly during baking. Cover with cling film and leave it for a minimum of 8 hours and a maximum of 12 hours. This will allow the semolina grains to swell. (This is how it is made in pastry shops in Beirut.)
Preheat the oven to 200°C/400°F.
Using a serrated knife, score the dough into equal squares or diamonds.
Add your favorite nuts to each square. They could be blanched sliced almonds, pine nuts, or cashews.
Bake the namoura on the lower rack of the oven for 20 minutes. At this stage, you will notice that the namoura has started to develop some color. Remove it from the oven and, once again, using a serrated knife, cut all the way through the marks you made earlier. Evenly drizzle the ghee over the top of the namoura.
Place the oven rack in the center position and return the namoura to the oven for an additional 15 minutes, or until the top is golden brown.
While the namoura is baking, prepare the sugar syrup. Place the sugar and water in a pot over high heat. Bring to a boil, stirring until the sugar has dissolved. Add the lemon juice, which will help prevent the syrup from crystallizing, and continue boiling over high heat for 2 minutes. Add the orange blossom water, then remove from the heat and keep the syrup hot.
Once the surface and bottom of the namoura are deep brown, remove it from the oven and immediately pour the piping-hot sugar syrup all over it. The namoura will absorb the syrup within a few minutes.
Set aside for 3 to 4 hours. Using a pie server or spatula, transfer the namoura squares to a serving plate.