Preheat your oven to 350 degrees Fahrenheit and butter an 8x8 inch baking dish.
Place the cubed day-old bread into the prepared baking dish.
Whisk the eggs, milk, sugars, cinnamon, nutmeg, and vanilla extract in a large bowl until smooth.
Pour the custard slowly over the bread cubes, pressing down to submerge them.
Rest the dish for 15 minutes to allow the bread to soak up the liquid.
Bake for 45 to 50 minutes until the center is set and the top is golden brown.
Melt the butter for the sauce in a saucepan over medium heat.
Whisk in the heavy cream and sugar, simmering gently for 3 minutes until thickened.
Remove from heat and stir in the tablespoon of vanilla extract.
Serve the warm dessert sliced with the vanilla sauce poured over the top.
