Grease 4 ramekins and preheat oven to 350º. Cut crusts off white bread and cut into 1 in cubes. Put bread into a bowl, pour milk and cream and toss to coat. Set aside. Beat eggs and pour in melted butter, sugars, and vanilla, stir to combine fully. Mix soaked bread cubes, egg mixture, and chopped plums. Pour mixture into ramekins. Place ramekins on a rimmed baking sheet and cover with aluminum foil. Bake for 20 minutes. Remove foil and bake for another 30 minutes or until just golden brown.