Put bread cubes into large bowl. Mix eggs, cream, brown sugar, zest and vanilla together; pour over bread. Mix well and let sit for a minimum of 15 minutes. Butter a casserole dish and pour the mixture into the casserole. Put into the top half of the oven until the center is slightly firm to the touch, about 30 minutes. Remove and serve warm, topped with whipped cream, blueberries, and powdered sugar.