Combine the flour, sugar, baking powder and salt in a large bowl. Make a well in the center of the mixture. Combine the egg, milk and oil then add the mixture to the dry ingredients. Stir until just moistened and no flour streaks remain. Spoon into muffin tins, that have been coated with a non-stick spray, filling each cup 2/3rds full. Spoon 1 ts of the plum jam into the center of each filled muffin cup. Bake at 375 degrees F. for 20 minutes or until golden brown. Serve warm.