1. Preheat oven to 170 c (325°F).
2. In a large bowl combine semolina, sugar, baking powder, sour cream and margarine.
3. Gradually add water.
4. Beat until smooth (a little more water may be needed).
5. Oil a large oven pan. Spread the pan with tahini.
6. Pour the batter into the pan, sprinkle with peanuts or pine nuts, and bake 45 minutes, or until golden.
7. Cool. Make syrup: combine sugar, water and lemon juice in a large, heavy-bottomed saucepan.
8. Cook on low heat for 20 minutes, until thick.
9. Cut the cake to 5 cm x 5 cm (2 inch x 2 inch) squares, and pour the hot syrup over the cake squares.
10. Serve immediately or at room temperature.