In a saucepan melt together butter and sugar. Remove from heat and let cool for a minute then mix through half a cup of the choc chips until melted then the eggs. Add flour and soda water and mix well. Once quite cool add another 3/4 cup of choc bits. Pour into a square cake tin and add blobs of jam on top. Swirl a little with a skewer and bake at 180 deg cel until just firm in the middle. Once cooled, melt remaining white choc and drizzle over.