1. Place all ingredients in a small saucepan and boil until the sugar dissolves.
2. Boil for 1-2 minutes, then remove from heat.
3. Let it cool.
For the Base:
1. Beat the eggs with the sugar and vanilla until fluffy. Add the bitter almond essence, brandy, and finally the pistachios.
2. Pour the mixture into a lightly buttered baking pan and bake in a fan oven at 175-180 degrees Celsius for 15 minutes.
3. Remove from the oven and pour the cold syrup over it.
Prepare the Cream:
1. In a saucepan, combine the milk and dissolve the cornstarch. Add the sugar and place on heat, stirring until it begins to thicken. Add the heavy cream and continue stirring.
2. Just before it thickens completely and you remove it from the heat, add the bitter almond essence and mastic (be careful with the bitter almond essence, as too much will make our cream bitter).
3. Spread the cream over the sponge cake and sprinkle with ground pistachios while it's still warm. Let it cool, then refrigerate.