In a medium mixing bowl, whisk together brown sugar, cinnamon, salt, and nutmeg.
Add eggs and vanilla extract. Whisk for at least 30 seconds, until the cinnamon is blended in as smoothly as you can get it.
Whisk in milk.
If you will be cooking in batches, set your oven to 170°F (or its lowest setting) and place a baking sheet or large oven-safe plate inside.
Melt 1 tablespoon butter in a large nonstick skillet or griddle over medium heat. Use a silicone spatula to spread evenly around the pan.
Pour egg-milk mixture into a wide shallow dish or baking pan.
Dip 1 slice of brioche into the egg mixture for 1-2 seconds per side, letting any extra drip back into the dish.
Repeat with 1 or 2 other slices, depending on the size of your skillet. Don’t crowd the pan.
Cook for 3-5 minutes, until the bottom is deep golden brown, then flip and cook the other side.
Transfer the finished French toast to the baking sheet in the warm oven.
Add another tablespoon of butter to the skillet and repeat with the remaining slices, adding more butter as needed.
Serve warm, topped with a pat of butter, maple syrup, and fresh berries, if desired.
Notes
Storage Tips: Store leftover French toast in an airtight container in the refrigerator for up to 4 days. Reheat in a nonstick skillet or in a toaster oven or air fryer until warm and crisp. You can reheat in the microwave, but you'll lose the crispy edges.Expert Tips:
Don’t skip the step of whisking the spices into the brown sugar first. Cinnamon doesn’t dissolve well in liquid, so adding it to the brown sugar helps it blend in and not float in clumps on the surface of the custard.
Keep the dip short. Brioche is soft and absorbs custard quickly. Dip each slice for just 1-2 seconds per side, or it will get soggy.
Love crispy French toast? Try sprinkling a little granulated sugar on top of each dipped slice before it goes into the skillet. Keep an eye on it, since sugar can brown quickly.
Slice the brioche yourself if you can. That way you can make sure your slices are the optimal thickness for French toast, around ¾ to 1 inch thick.