Put the butter in a heavy-bottomed pan on the heat to melt. When nearly completely melted, stir in the chocolate. Leave for a moment to begin softening, then take the pan off the heat and stir with a wooden spoon until the butter and chocolate are smooth and melted. Now add the cherry jam, sugar, salt and eggs. Stir with a wooden spoon and when all is pretty well amalgamated stir in the flour.