Hi, judging by the size of your dish you are confusing bread pudding with bread and butter pudding.. I make both .
Differences, bread and butter pudding is usually made with slices of bread and butter, and served warm with custard whereas bread pudding which is made in a loaf pan is much darker in color and is served cold and sliced like most sweet loaves.
I think it is bread and butter pudding you are requesting.
Personally I don't have a written recipe I just wing it but here goes.
Slice your bread not too thick sort of like commercial sliced bread, you can make it with crust or crustless as you wish, personally I remove them. Your challah already has some good stuff in it so it will be fine. Butter it both sides, cut your slices into triangles, then place in your dish points up, sprinkle raisins and white sugar between as you go as many as you like .
In a decent sized jug blend eggs , milk, cream and whatever spices you like . I usually use cinnamon but sometimes use nutmeg,apple pie mix or English mixed spice but don't overspice it, you want to taste the egg etc. It is hard to tell you exactly how much of each wet ingredient I tend to be quite heavy with the wets though and make enough then when added it looks quite soggy. Make sure you pour slowly so the sticky up points get well moistened. It will be moist when done. Less eggs and it will be softer, more eggs and it will be more firm, either way is should not be dry
I don't cover because I want the points of my pudding to brown nicely, I cook in a 335ish oven, it is not crucial , when the eggs etc are set and the crust tops are nicely brown it is done.
If you need a more detailed recipe let me know and I will make one tomorrow or the next day and write it as I go.
If you want the bread pudding one let me know too, it is quite heavy and traditionally designed to use up all the stale bread.
XX Jeannie