In a microwave-safe bowl, combine the milk, heavy cream, and half stick of butter.
Microwave for about 1 minute, or until the butter is fully melted.
Carefully pour the warm mixture into a large mixing bowl. Allow it to cool for 1–2 minutes so it doesn’t scramble the eggs later.
Whisk in the eggs and light brown sugar until smooth and well combined.
Add the vanilla extract, pinch of salt, cinnamon, and nutmeg. Whisk again until the mixture is silky and slightly frothy. You can adjust your cinnamon and nutmeg to your liking.
Slice your brioche into thick slices (about 1 inch is ideal for a custardy center).
Heat a large nonstick skillet or griddle over medium heat.
Add 1 tablespoon of butter and let it melt until bubbly.
When your pan is ready, dip one piece of bread into your mixture 10-20 seconds per side. You do not want your bread to be completely soaked.
Place the soaked brioche slices onto the skillet, letting any excess custard drip off first.
Cook for 3-4 minutes per side, or until golden brown and slightly crisp on the outside.
Add more butter as needed between batches.
Serve the French toast warm with maple syrup, fresh berries, whipped cream, or a dusting of powdered sugar.