Step 1

Pour milk into a large saucepan, and bring to a boil over medium heat. In a medium bowl, whisk together the semolina, cornstarch, 1 cup sugar and salt so there are no cornstarch clumps. When milk comes to a boil, gradually add the semolina mixture, stirring constantly with a wooden spoon. Cook, stirring constantly until the mixture thickens and comes to a full boil. Remove from heat, and set aside. Keep warm.

Step 2

In a large bowl, beat eggs with an electric mixer at high speed. Add 1/2 cup of sugar, and whip until thick and pale, about 10 minutes. Stir in vanilla.

Step 3

Fold the whipped eggs into the hot semolina mixture. Partially cover the pan, and set aside to cool.

Step 4

Preheat the oven to 350 degrees F (175 degrees C).

Step 5

Butter a 9x13 inch baking dish, and layer 7 sheets of phyllo into the pan, brushing each one with butter as you lay it in. Pour the custard into the pan over the phyllo, and cover with the remaining 5 sheets of phyllo, brushing each sheet with butter as you lay it down.

Step 6

Bake for 40 to 45 minutes in the preheated oven, until the top crust is crisp and the custard filling has set. In a small saucepan, stir together the remaining cup of sugar and water. Bring to a boil. When the Galaktoboureko comes out of the oven, spoon the hot sugar syrup over the top, particularly the edges. Cool completely before cutting and serving. Store in the refrigerator.