Cut the bread slices into 1” cubes and put them into a buttered 2 qt. casserole dish. Heat the milk until just boiling in a saucepan, then remove from heat and stir in the butter until melted. Pour this over the bread cubes and let sit for about 15 minutes.
In a separate bowl, mix together the eggs, sugar, salt, cinnamon, and rhubarb. Pour this over the bread mixture and combine. Top evenly with the brown sugar.
Bake for 1 hour or until set. Let stand about 20 minutes before serving. Serve warm with the additions of your choice, and enjoy!