Slice the challah into 1½” slices. Empty the Custard into a wide mixing bowl or baking dish, big enough to at least fit a whole slice of the challah. Now set a griddle pan or large saute pan over medium-low heat, with a little butter or neutral oil. While heating, work with one or two slices of challah at a time: lay the slice in the custard, soak for 30 seconds, then flip and soak on the other side for another 30 seconds. Lift the soaked slice and let drain for a few seconds, then place on the hot griddle or pan.
Cook in batches, getting a nice golden brown on one side, then flipping. We want to cook medium-low heat here so the eggs soaked through the challah souffle. Too hot, and you will get golden brown outside but raw in the middle. If it seems like it is cooking too fast, reduce the heat to low and let is do its thing. Once all slices are cooked, top with compound butter, fruit, maple syrup and powdered sugar.