In a large mixing bowl whisk eggs, cream, milk, orange juice, zest, nutmeg, cinnamon and vanilla until eggs are beaten and mixture is well combined.
Dip Challah slices in egg mixture and layer in a buttered 9” x 13” casserole dish. Pour remaining mixture over the top and press down.
Cover and refrigerate overnight.
Preheat oven to 350ºF.
Uncover casserole, dot with butter and bake for 35 minutes or until top is golden brown.
Serve warm with sour cream and marmalade, mascarpone with jam, maple syrup, fresh fruit and/or whipped cream.