Preheat oven to 355F/180C.
Sift flour and sugar into a large bowl.
Place butter in a small saucepan and heat over low heat until butter is melted.
Add butter, milk, eggs and vanilla to flour and sugar mixture.
Stir with a wooden spoon until well combined.
Pour into a square baking dish lined with parchment paper (note 3)
Bake 30 -35 minutes, or until golden brown.
Poke the middle with a sharp knife, if it comes out clean the cake will be cooked.
Cool on a wire rack.
Once cooled, cut the cake in half using a sharp knife.
Evenly spread raspberry jam over bottom layer of cake, making sure it comes out to the edges without over flowing.
Place top half of cake on jammed half.
Dust with sifted icing sugar and serve.