Whisk the melted butter with the maple syrup and 1 tablespoon of light brown sugar. Pour into the bottom of the greased pan.
¼ cup maple syrup, 4 tablespoons unsalted butter, 1 tablespoon light brown sugar
In a large bowl, whisk the eggs with the milk, heavy cream, vanilla, rest of the light brown sugar, cinnamon, nutmeg and salt. The cinnamon will float to the top but that is normal! Place each slice one at a time into the bowl for at least 10 seconds to soak up the custard mixture. Arrange the slices in the baking pan.
½ cup light brown sugar, ½ tablespoon vanilla extract, 1 ½ cups whole milk, ¼ cup heavy cream, 6 large eggs, ½ teaspoon kosher salt, 2 teaspoons ground cinnamon, ½ teaspoon ground nutmeg, 1 brioche loaf
Pour any remaining custard over the bread.
Overnight option: cover with clingfilm and chill overnight.
Preheat the oven to 190°Celsius/375°Fahrenheit and bake for 45-50 minutes. If it starts to brown too much then cover with foil. If you have chilled it overnight be sure to take off the clingfilm first before placing in the oven!
Serve with fresh fruit and maple syrup.
Notes
My recipes have been developed and tested in cups and metric grams. I highly recommend using a weighing scale and measuring out your ingredients the metric way.Brioche: it is best to use sliced brioche which is slightly stale, but I have also tested this with fresh brioche bread and it still tasted amazing! You can also use challah. You want to use about 15 oz of bread.Storage: keep the cooled french toast casserole in the fridge for up to 2 days, you can reheat in the microwave or in the oven.