Lightly toast the brioche in a standard toaster, toaster oven, or oven until crisp and dry but not browned. To toast in the oven, preheat to 375F. Set slices on a cooling rack placed over a Sheet Pan and toast 6–8 minutes, flipping halfway through.

Add the eggs to an Entrée Bowl or Pie Dish and whisk until smooth. Add the eggnog, sugar, cinnamon, vanilla, salt, and nutmeg (if using). Whisk to combine.

Preheat a Carbon Steel Griddle over medium-low. Dip each slice of bread into the custard, coating both sides and letting it soak about 1 minute. Add the butter to the griddle to coat the surface. Cook until golden brown and set, about 2 minutes per side. Add more butter as needed during cooking.

Serve warm with raspberries, powdered sugar, and syrup, if desired.