Slice the challah bread into thick slices and let it sit for at least 2 hours in a dry area, covered. (A little bit of stale will help hold in everything and make for perfect French toast),
Whisk the eggs and half and half with the cinnamon, sugar and vanilla.
Heat a skillet or griddle to cook the French toast.
Line a baking pan with a wire rack and preheat the oven to 200 degrees F.
Dip the bread slices in the egg mixture and let sit for 15 to 20 seconds, flipping once. Remove and let sit on the wire rack.
Melt the butter on the preheated skillet and fry the slices of bread until golden brown. Keep warm on an oven safe platter in the preheated oven until all slices are cooked.