Preheat oven to 180 degrees C. Grease and flour a 20x30cm pan. Sift together the flour, baking powder and powdered milk. Set aside.
Cream together butter and sugar until light and fluffy. Beat in eggs, one at a time, then stir in the vanilla. Stir in the flour mixture until incorporated. Batter will be thick.
Pour batter into prepared pan. Bake in the preheated oven for 40 minutes, or until a toothpick inserted into the centre of the cake comes out clean. Prick cake with a fork at 3cm intervals. Allow to cool.
For the glaze: In a saucepan, combine the sugar, water and instant coffee. Bring mixture to a boil, and cook for 2 minutes. Pour the syrup over the warm cake. Cool thoroughly.